Am i the only one that thinks we havent seen the last of Cain? I dont want to see him come back as an evil undead boss character, but Zoltan kulle was a Horadrim, and was so hard to kill that they had to do all kinds of crazy stuff just to disable him. Cain must have learned some magic from all his research other then being an endless supply of identify items, maybe he prepared for his death in his old age to grant him some kind of rebirth, there is always the possibility that he will be granted some power amongst the angels because of all he did to fight Diablo. I dont know just seems unlikely to me that Cain wont be seen again.
Honestly i was a bit surprised we didnt see the return of Deckard in the ending scene somewhere.