Well, we've heard mention of Hell--whether Jacob intended that to mean the MIB or not, I'm not sure. But since Hurley via Isabella said that they'd all go to Hell if the MIB is not stopped I take it to mean that being overcome with him, i.e. Sayid and Claire, is Hell.
There's no mention of Heaven, but maybe just not being overwrought with malevolence is Heaven, in a sense. Yet, Jacob was puzzled over whether people tended toward good or evil so can assume that he's missing some overall info. But who/what is he (and the MIB?)--and what are humans for that matter, that they contain this mystery?
Anyway, my intention for this blog was to question the wandering dead people. If Hell is blocked up then maybe Heaven is, too, and no one can venture to either place afterward. Although, I'm leaning toward Heaven and Hell being a state of aliveness. But then, why not just be dead? YET--Jacob told Richard that he couldn't stop him from going to Hell--which sounds like maybe they're playing at a game of salvation here...Jacob wishes that none should perish, and they have that choice, and the MIB just wants to claim them all before they have a chance to reverse their state of being born in sin, shaped in iniquity. Bit of Biblical reference there, but it fits the bill.
This is all jumbled and not thought out well enough, but please garnish me with your thoughts on the matter(s) :)