Two questions: Do you think we will meet Mephisto and Baal in Diablo 3? Do you want to meet them in Diablo 3?
Seeing how they can bring Diablo back, even though we allready killed him, they shouldn't have any problems with these two if they wish to include them in the game. I am torn. Diablo wouldn't feel the same without them, but I guess it would be kind of repetitive with them.