Yes, but are theories i would like to believe that sora will be in the next game...
but, there are rumor that the next game is a lot of years later where is a fight over the ultimate Keyblade or something like that, there is other theory that its a lot of years later and there is a new "choosen one"
Well, about Roxas i knew he was ******* for a simple but hidden clue on his name, (easy to guess) i liked a lot the plot (very slow at the beginning).
and
That might also explain Xehanort's heartess having cloths similar to the villain in this game and riku's dark cloths begin similar to the accomplise, they might have been based on that clothing.
I think they explained the xenahort heartless, something like, when he was training with ****** his tutor (if u won KH2 will know whos hes tutor)
he experimented with his body and became a heartless and a nobody<--- i undertood something like that, sorry if it is a Spoiler