That is, nothing.
I agree with Christopher Hitchens that religion is shameless in its manipulations of death fears via the carrot and stick of heaven and hell: it really is a moral outrage. One should never claim more about death—or anything, for that matter—than you really can know. But I think that Hitchens then claims more than he really can know.
I’m forgiving of Hitchens, however. Obviously his motive is to offer a salve to the psychologically oppressed: a blessed assurance—via Epicurus—that hell is not in the offing, but only a dreamless sleep. But he doesn’t know. Hamlet was more cautious (and rightly confused):