I think Bach will be beaten by someone, maybe Ichigo, but SS will turn against Ichigo or maybe the RG because i remember what Kyoraku said about Ichigo maybe having to stay there. Ichigo won't accept it and neither will most of the mains characters so they might have to fight there wayh out or something. only way I see all our favs getting screen time.
As much as I would like it to be, I don't think it will be Aizen. While his return is hinted at to happen, I doubt he'll come back just to stir up trouble, given how many Shinigami and Quincy will be up there with him if he tries anything.