Well, I don't think Sora will sacrifice himself. Nomura said the games are always going to be Sora's story, and the Xehanort chronicles are only the beginning. I just hope Riku doesn't... ;A;
I think it will involve defeating the real Xehanort, then having to fix Kingdom Hearts in some way. It seemed to be full of Heartless; maybe it needs to be unlocked with Keyblades and washed in light or something? Maybe Sora will have to go to all the worlds and make the people of the worlds do something that will help him (like everyone singing the hymn in FFX
) and flood the universe in light that could heal KH?
Also Kairi's grandma's story has been repeated twice now, so I think it will be important after all. All the worlds will be put back together into one.
Cheesy or not... I don't know, but I've always thought KH is pretty cheesy. That's part of where the nostalgia comes from. So, I wouldn't care if it was cheesy.