Former DC honcho and current Doomsday Clock writer Geoff Johns has killed Jonathan Kent twice and Martha Kent once in the last decade or so, but now some are thinking that Superman's adoptive parents may actually be alive in the current continuity -- and Superman writer Brian Michael Bendis isn't saying one way or the other. That's per Newsarama, who recently found themselves wondering what Doctor Manhattan's interest in the Kents was in Doomsday Clock #10. Their theory is that the Kents may be revived as part of the events of Doomsday Clock, a series which was originally set one year in the future of the then-current DC Comics universe.
The idea was that Doomsday Clock would run for a year, during which time the DCU would catch up to them and events could spring out of the story's fallout. Instead, the title has been running consistently late, and will end about a year after it was originally supposed to. Given the long-term planning going on at DC right now (Bendis recently suggested that he has at least 25 issues of Legion of Super-Heroes planned, while Tom King has had a 100+ issue Batman story in the works since he was on about issue #30), it seems plausible that current comics could be quietly working out elements of Doomsday Clock which were supposed to have been resolved by now.
In the pre-Crisis on Infinite Earths DC Universe, Ma and Pa Kent had died before Clark left for Metropolis, and were only a significant factor in Superboy stories. Some tales had Ma alive after Pa had died, which was what Richard Donner's Superman: The Movie did. It was that film that inspired Geoff Johns to kill off Jonathan Kent during the best-selling "Brainiac" story in Action Comics a few years back.
He was able to do that because when John Byrne rebooted Superman in the mid-'80s, his reworked origin kept the Kents alive and made them a part of the ongoing series. Clark could use them as his sounding board and, until Lois eventually learned his secret, they were some of the only people he could talk to when he needed someone who really understood what he was dealing with. They remained a part of his life until Jonthan's death in "Brainiac," and then a couple of years later, the 2011 line-wide "New 52" reboot included an origin that revealed Jon and Martha Kent had died in a car accident years before Action Comics (vol. 2) #1.
That accident appeared in a dream in Doomsday Clock #1, and their deaths (and non-deaths) were something that Manhattan commented upon when he was watching time break and then heal itself over and over again in Doomsday Clock #10.
Recent issues of Young Justice (by Bendis) have obliquely referenced Superboy (Conner Kent) as having gone to Smallville High School very recently. In the pre-New 52 continuity, the character had been sent to Smallville to be raised by the Kents during a very low point in his life when he needed guidance. While not explicit, the Young Justice issues seem to confirm that's what he was doing in recent months in Smallville, which implies that the Kents were alive as recently as a few months ago, and did not die while Clark was in high school. Bendis also wrote a scene in the recently-published Superman #11 in which Clark talks about Martha Kent in the present tense, arguably suggesting that she was alive as of the events of that story.
Confronted with all of this, Bendis told Newsarama, "I'm very excited you asked me that. I can't answer that question until all of Doomsday Clock is revealed. Just to be fair, that train had left the station before I was even at DC. So I have full respect for making sure that story gets told the way it needs to get told."
So...just a few more months, perhaps, for the end of Doomsday Clock and some answers about the state of a lot of things in the DC Universe...including the Kents.