I was just reading about Algalon the Observer on WoWWiki (yes, procrastinating): http://www.wowwiki.com/Algalon_the_Observer
If you look at his text when he despawns (he can't be "killed"), he sends a signal to the Titans for "re-origination" (i.e. wipe Azeroth clean). I wonder if this could be fodder for a future expansion. If not for the next one, maybe for the one after -- battling the (*cough*Norse*cough*) gods does seem fitting for level 100, eh?