Diablo III Designer Explains Why Necromancer Was Cut, Hints At Return on MTV Multiplayer justifies cutting the Necromancer class from the action/RPG sequel, and hints that this may not be a permanent situation: The reason it was cut was because they didn't want to rehash the characters from previous Diablos (the Barbarian returns because they thought they had a new take on the character), but lead designer Jay Wilson indicates this was not a universal opinion, even among the Diablo III developers, so the Necromancer may eventually be, yes, resurrected:

“There’s a lot of people on our team who aren’t happy with our class choices,” he admitted. “But after we’ve established ‘Diablo III’ as its own game with its own type of gameplay and experiences, I wouldn’t be opposed to looking at old classes. We are trying to design [the Witch Doctor] class so that if we did bring back the Necromancer, there’s room for him. We’re looking out ahead of time at what our expansions are going to be, so we’ve got to keep room open for some of those other classes down the road.”