Does everyone left behind at the EotA planet die from the apocalypse or are there (lore shattering!) easy to achievement ( =single person ) means to escape to another world which are used by some of our heroes who are still in peril?
And how long is the time between the end Exodus and the apocalypse?
Hrm, to answer that, I need to describe what the apocalypse is.
Basicly, back on elf world, after the bulk of them fled to orc world, the survivors (mostly the elven army, but various other stragglers that got left behind) managed to retreat away from the place of the final stand. As you may recall, the closing of the portal caused a massive explosion which "killed" (remember, demons respawn) most of the demon hordes. The demons generally presumed the remaining elves were dead. Instead, they fled off to the coast to some smallish island, then errected a magical barrier to hide themselves.
Over the following centuries, a few things happened. First, the survivors became extremely resentful of those that made it through, turning from "I'm glad most of us got out" to "why the fuck did they leave us behind? they ought to come back and rescue us now." Second, and related to the first, the demons ultimately did find their hidden island, but only a few demons found out and the elves didn't generaly know it happened. And the ones that did happened to be the trickey manipulative types. So they ended up speeding up/worsening the resentment, and generally slowly corrupting elven culture in general.
Note: Why didn't they create a new portal? The old one's collapse was designed to prevent the demons from trying to follow, so it majorly fucked up all forms of portal travel in both worlds. It slowly improved over time, but still only very small, short distance portals are viable.
So finally we reach more recent history. I'm not going to say the elves are like drows now, but thier pretty different then the old elf culture. Their population has also grown, their stuck on their tiny ass island, their surrounded by demons and they're grown to hate those that got to the other world. Their solution? Send/lure the demons to the other world. If possible, then destroy said other world; at the very least, trap them all over there. There is your apocalypse.
So the old elves manage to communicate to the other world and start this prophecy to convince the survivor elves to reopen the portal and come back, thus sealing their doom. No, I'm kidding, that's too cliche. Some of the lesser corrupt elves got wind of the plan and thought that was a bit too extreme. While the elves are trying to put their plans in motion, this "rebel" faction instead decides to use the work in progress to send warnings to Orc world that their world is doomed and they need to come back and help them retake Elf world from the demons. Really only the first part of the message gets through, but it unintentionally has the same effect of getting Orc world elves to get the idea to flee back to thier old world.
So what does happen after exodus? Well, the portal reopening plus the old elves' plan does end up luring a substantial number of demons to Orc world (although elf world is by no means safe). This, combined with the complete lack of remaining societal structure in Orc world means it's a huge fucking mess nobody wants to stay in. The old elves plan to physically destroy Orc World is put to a stop by a mix of heroes (AM/AA, SB join together with some new heroes from a map that never got made), so Orc world continues to exist.