I know there has already been a recent thread on this, but there were that many posts (which people dont read) that nobody would see mine.
Anyway, as far as i'm concerned, the Emperor, the one and only, dies in Warhammer 50k, where the big new purple thing comes (i dont know what its called but its big enough to devour terra) and chaos and Tyranids practically over-run the galaxy.
So, what i think happens is:
1) The big purple thing kills everyone on Terra, killing Zhe Emprah
2) Abbadon dies ages ago
3) Most of the space marines have died and there are only about 50 chapters left and all are between 10 and 200 strong
4) Tyranids come from other galaxies and take a third of the galaxy
5) All of humanity is divided into several factions, spread throughout the galaxy, un-able to communicate some sort of inter-joined defence
6) All other races such as Tau, Necrons and Eldar etc are all beaten up a lot, like the remnants of the Imperium
7) The orks regain a lot of land
8) chaos have wars from within, each god at war with each other
9) practically the end of warhammer, big epic battle at the end
note - This is (possibly wrong) info that apparently leaked that i found out 2-3 maybe even 4 years back. I cant remember where i found this from but i remember it in detail of what it's about, like said, it could be complete bull

but it's just something i had to let out.