If you haven't read the End if times rumor thread. Here is a post by Archibald_TK

What the background in the WD tell us:
- I hope you didn't like Kislev, because there is no longer a Kislev.
- Archaon advance have been stalled by Vlad under the order of Nagash (the Empire was in major trouble).
- Nagash goes fighting to unite the Tomb Kings and VC (one of the scenario pictured in WD translate into "the Fall of Settra").

Kislev was wiped out by Archaon.....completely never to return. Tomb kings seem to be next on the chopping block. The Empire and Valten were putting up only a doomed small resistance till VLAD himself returned to claim all the dead and drive back chaos. If you hated the Grimgor bit you can rest easy, as in the end Archeon still won and was only stopped by Vlad...after he ended Kislev.

Both the high elves and dark elves are facing their doom by massive daemonic invasions. End times level invasions. We wanted the storyline to advance and it did.