500 - yeah, Sasuke will return. That is, if Naruto get's through step one of training and step two requires effort rather than inner reflection. Couldn't they just do his training like this:
http://www.youtube.com/watch?v=FIi0vFyqWAc
As for Madara - we won't see his mask until he actually fights someone who can hit his face and bust it off. I don't think there will be a voluntary reveal as I think he would have done so if he had wanted to.