Starting with the least likely and escalating--and please do understand that these odds have no basis in any kind of mathematical reality at all, except that it's what we'd personally set them at if we were go gamble (which we don't) and had that kind of money (which we don't).
So for the love of all that's holy, don't actually take these numbers as meaning anything other than "More or less likely than the person immediately above or below them on the list."
Rick Grimes (1,000,000 to 1)
He's the main character, and the face of the franchise in all of the marketing. Plus, anything horrible that happens to the rest of the group will reflect on his leadership and weigh on him. Additionally, people involved with the production have said that next season, his leadership will be called into question. Little point in that if he's dead.
He's the Arthur Fonzerelli of the series; while Rick may be the nominal main character, it's Daryl the fans really want to see. And while that may raise some uncomfortable questions as to whether Merle is Chachi or Pinky Tuscadero in that equation,
Michonne (500,000 to 1)
Well, we know for sure that neither Michonne nor Andrea die in episodes 14 or 15, because Danai Gurira said at Emerald City Comic Con that she knows where the story takes those two characters in episode 16 (the season finale). But once we get there, what are the odds?
Much better for Michonne, who is a fan favorite, the strongest nonwhite character on the show and--this is key--the Governor's favorite target, so killing her would give the bad guys a major "win."
Carl Grimes (100,000 to 1)
Sure, he's still alive and kicking in the comic. And sure his death would absolutely devastate Rick. So why is he more likely to go than Daryl and Michonne?
Simple: Eventually the problem of Chandler Riggs growing up on camera will catch up to you in a TV series. Keeping Carl alive and pushing the story forward months or years at a time only really works if the showrunners think they've only got a couple of more years in them.
By far, the most likely member of the Greene clan to make it out of this season alive. Especially because rumor has it she'll be getting married to Glenn in an episode coming up, which makes it a lot less likely either of them will kick the bucket soon.
Glenn Rhee (1 to 10,000)
Less likely, but not impossible. Why give Glenn such a massively lower chance of survival than his betrothed? It's simple, really: He was recently and brutally killed in the comics. Now, if they foresee themselves going up against Negan in a tentative season five or six, then absolutely they'll hang onto Glenn to make that story more dramatic--but there's nothing to say that role won't be filled by another character and that Glenn can't still be in grave danger.
Tyreese (100 to 1)
While he's played almost no significant role up to this point, the death of Tyreese--a fan-favorite character played by a well-liked actor--could be a key moment in the finale if played right.
Still, his relationship with Michonne in the comics (and the scene of clearing the gymnasium) were defining features of the character, and to have him dispatched so quickly without either of those ever happening seems like a waste. We're betting he's around for a bit longer, especially since three episodes doesn't seem like enough time for him to be so completely alienated from the Governor, and endeared to the prison, that killing him in the way the comics did would make any sense at all.
Probably saved by virtue of her relationship to Daryl. We don't think Merle is going to make it, and taking essentially his entire support network away from him would be just absolutely nutty.
Dr. Stevens (50 to 1)
Much like black, male leads on The Walking Dead, there can be only one doctor. If Hershel makes it, the chances are good Dr. Stevens will die valiantly while trying to save one of her people either in Woodbury or at the scene of the battle, which we're assuming will be the prison.
Hershel Greene (50 to 1)
He's one-legged old man, so you'd expect him to be pretty much dead, right? Well, he's proven himself to be resourceful and resilient, and we still think the whole guns-duct-taped-to-the-stump thing was foreshadowing for a key moment. Will he survive the finale? It's really hard to say, but we thing his odds are better than most would give him credit for.
Allen (10 to 1)
If Hershel lives, one could plausibly see Allen taking on the death that eventually befell Hershel: to be killed while mourning the loss of his son in battle, too emotionally crippled to respond or fight back. Ben is a bit like Jimmy last year: he's been standing around, not saying much, just waiting for a time when his death can mean something to Allen and Tyreese.
Honestly, this one could go either way. In the comics, she's still around and is a huge part of the cast--but the TV series hasn't treated her well, and from the word go, we've pretty much assumed that either she or Merle would take out the Governor--and whichever one didn't, would die trying. Having her up here means that Merle is pretty far down the list, with the odds looking pretty grim for ol' Stumpy...but the writers could surprise us and give us a world where Merle walks away and Andrea doesn't.
After all, just having the Dixons around changes everything. Do we really need another "permanent" member of the cast when we've got Daryl to fill her role?
The Governor/Philip Blake (1 to 1)
Should he be further down this list? Well, it depends on what their plans are for next season, which are pretty unclear at this stage. The Governor is either dead at the end of the season, and the group likely moving on from the prison (which series creator Robert Kirkman has appeared to tease), or he's not dead--and there's another season of dealing with Woodbury on the horizon.
Why's he so high on the list, then? Well, because frankly Kirkman loves the Governor; he and Jay Bonansinga have written what is now a trilogy of prose novels based on the character, in which familiar faces from the cast of The Walking Dead show up only in passing. He's long been the fans's favorite villain and is still arguably the most formidable threat the cast has ever faced (the comics also have Negan, and Kirkman would very much like for fans to believe he's more bad-ass than the Governor, but honestly it's like Darth Maul to Darth Vader: you can make him look awesome and give him cool props, but at the end of the day he's still a pretty pale imitation of the classic).
So clearly this is a character in whom Kirkman sees a lot of potential and a number of stories.
Karen (1 to 10)
One of the Woodbury wall guards, she tried to escape when things got ugly and then failed to stop the Governor from drafting her teenage son into military service. It's hard to picture a scenario where she doesn't go into battle with him (even though she's female and so wasn't drafted, she's still been a guard and will want to go protect her son) and then lose it and end up killed by one side or the other (or walkers) when her kid is endangered or dies.
Noah (1 to 20)
He's 14, he has asthma, and he's one of the only Woodbury characters about whom the fans know anything besides, "He was there when such-and-such an event happened." That's just begging for him to be one of the first fatalities, before things get really out of control, so we can see his mother's horrified reaction.
The loss of Beth would be absolutely crippling for Hershel and Maggie, and do quite a number on the rest of the group--but it wouldn't really have much impact on the chemistry of the show, since her primary role this season has been to sit around, take care of the baby and sing. So if you're assuming that the baby's survival is in doubt (we are), what purpose does Beth serve again?
Sasha (1 to 50)
Another case of, "Does anyone know anything about her?" She's the girl with Tyreese. That's it. Occasionally she talks. Killing her would have a huge impact on Tyreese if he survives but leaving her alive would give the writers almost nothing. Taking away Allen, Ben and Sasha all in the big battle and leaving Tyreese a man completely without his people would certainly have some impact on the potential for stories with that character going forward.
Merle Dixon (1 to 100)
Let's face it, folks--as much as you like Merle, he's a white supremacist who is not a series regular, played by an actor with a lot of other commitments. The odds have always been good that he would end up worm food by the end of the year, and having betrayed the Governor, the odds start to really skew that way--especially if you assume (which we do) that Michonne and Rick, the Governor's other major targets, are pretty safe.
Ben (1 to 200)
Allen isn't stable enough to be a great protector for his son--we've already seen him try to steer the family into trouble by trying to take over the prison. Now, they're in Woodbury, where people don't tolerate that kind of thing.
With Milton--or rather, Dallas Roberts--it's really just dollars and cents. He's already signed a deal to appear in another TV series, andn so it would be nearly impossible to steal him out of that contract to bring him back next year. That's why his odds are so long--frankly, being part of the Governor's inner circle and also emotionally conflicted about the war are two things that make him hugely vulnerable if the two groups go to war and it's a final, decisive battle. If the battle isn't decisive, and we're back for another season of this, Milton is one of the most likely to go.
Caesar Martinez (1 to 1,000)
He's the main bad guy's #2 AND has been a huge jerk all season long. He's unstable, violent and not particularly kind to his own people. Look for him to catch friendly fire, and/or die a death that can be seen as karma.
Shupert/Bowman (1 to 2,000)
He's been known by two names, according to The Walking Dead Wiki.
The only guy more likely than the Governor's right hand man to die in battle is the Governor's right hand man's right hand man. Bowman has beeen around all season long; he's immediately identifiable, but most fans don't know his name. He's also, by his silence, complicit in the heinous acts of the Governor and Martinez for which he's present. He probably won't die the same kind of big, satisfying death you're likely to get from characters like the Governor and Martinez--but he will almost certainly die in the big "kill-em-all" battle.
Judith (1 to 25,000)
If our guess is right, the next few episodes are going to be emotionally raw for everyone; don't expect any major character who survives to do so without at least one major loss. The Governor may lose his best men; Michonne may lose Andrea; Hershel may lose Beth; Daryl may lose Merle--and on and on.
What makes Judith the most likely victim?
Simple: she's an infant in a war zone; there's no one to protect her, and the sound of her cries will draw both living and dead enemies of Rick's camp to her position. That puts her and her caretaker (which has been Beth most of the season) in huge jeopardy, even if it weren't for two key facts:
In the comics, Judith (and Lori, but who's splitting hairs) died during the final battle with the Governor at the prison, and...
Outgoing showrunner Glen Mazzara has said himself that every writer on staff wants to kill that baby, and he's the only one holding them back. To Mazzara, she represents hope and light, and he's not sure that he wants to be the kind of guy who snuffs all that out.
But it isn't his show anymore.
There are a number of extras in Woodbury, too, who seem like they're just primed to be cannon fodder, but who are still technically named characters. We'll list those here and give them about the same odds as we give Judith, since knowing very little about them it's impossible to differentiate them all:
Paul (pictured), Rowan, Ms. McLeod (more if we can track down names for any of them).