They didn't kill him off in JSA, and based on the way "Thy Kingdom Come" ended, his story is done.The absolute only character I care about is the Superman from Kingdom Come, currently residing in JSA. If they kill him off, as is rumored, I will just stop reading DC...
Once the JSA defeated Gog and tore his head off, he and Starman interred Gog in the Source Wall, and Starman sent Superman back to the ending of Kingdom Come. He arrived when the bomb detonated -- the implication being that his transition to the "main" DCU is what saved him (since Power Woman got fragged by the bomb) -- and then went on the rampage as we saw in Kingdom Come. The important part is not the retelling of Kingdom Come's ending, but rather what becomes of Kal-El after even the epilogue to Kingdom Come -- he learns how to be "human" again.
He can't die, not without retconning the end of Thy Kingdom Come, as Kal-El is shown as being alive to see the Legion of Super-Heroes. At the time, I assumed the Superboy-character in the Legion shown in Kingdom Come was Connor Kent, to use his later name, but chances are, based on Thy Kingdom Come, that it's a descendant of Kal-El and Wonder Woman, in shades of DC One Million and its descendants of Superman.