Potential spoilers ahead? We guess?
Based on the cover to Heroes in Crisis #1, which was solicited before the "one of these people will die" advertisement came along, ComicsCovered believes Kyle Rayner will be the hero to kick the bucket.
To be fair, this is more or less the same conclusion we came to, given that most of the other characters appear to have things going on in the near future at DC.
Going backwards: Heroes in Crisis, by Tom King and Clay Mann, is a series about Sanctuary, a psychiatric facility that services the superhero community. In the first issue, there will be a mass killing onsite, leaving at least two major characters and a number of minor ones (including, probably, one of the villains known as the Tattooed Man) dead.
The series will be a murder mystery in which point of view characters Booster Gold and Harley Quinn are suspects, so it was something of a surprise when DC included them on a list of heroes who might be dead on Sept. 26, the day the first issue launches.
The Reddit theory goes that of the six characters spotted on the cover of the DC Nation issue that teased a non-Flash death, five of them are visible on the cover of Heroes in Crisis #1. The list includes Tim Drake, Cyborg, Booster, Harley, Roy Harper and Kyle Rayner.
Rayner's absence on the title, and the presence of the other five, has fans assuming that Kyle is the one who will die in the issue. It's a solid piece of detective work, but there is one minor flaw in the argument.
Along the way, writer Tom King hinted that a Flash will die in Heroes in Crisis, and a recent issue of The Flash more or less confirmed that it was Wally West. That Wally is standing right near the center of the big crowd scene on the cover of Heroes in Crisis would seem to suggest that the victims are not necessarily singled out by their presence or absence on the cover.
Kyle nevertheless seems like the likely candidate. At the time, we argued as much.
The fatality is unlikely to be Booster or Harley, since DC has previously said that those two are the suspects in the attack, which lies at the heart of the story.
Given that Wally West is probably dying, betting against Roy Harper's death seems like a wise move, since gutting that generation of Titans all at once would be a strange move and likely very unpopular with fans. The same can be said for Cyborg, who was obviously a member of the Marv Wolfman/George Perez New Teen Titans generation — although he's also probably safe because of his status with the Justice League. Practical concerns might make it more difficult to get rid of Cyborg so soon after the League lost two characters of color and replaced them with one (the Green Lantern replacements).
That leaves Tim Drake and Kyle Rayner. If we were to make a bet, we would likely say Kyle is the most likely fatality, since Tim just got back from the "dead" — he was kidnapped by Mr. Oz at the end of the first Detective Comics arc of the Rebirth era, and did not return until about six months ago — but the flipside of that argument is that being dead for a long time and back for a minute seemingly did not prevent DC from targeting Wally West for elimination. Kyle might also be a candidate because Grant Morrison is taking over the Green Lantern titles for what we are assuming will be a fairly significant reboot.
Heroes in Crisis #1 will be released on Sept. 26.