I haven't thought that much about the future of the Dragons of Earth, except that they may all die, and that the Dragons of Heaven will live. I only base this assumption on the first few pages of the manga series itself, showing Kamui and all the Dragons of Heaven alive, and Kamui saying "He is my prey." Wouldn't that be a nice change for a CLAMP manga ending? But looking at their other works, I highly doubt that this series will have a happy ending. God knows the movie didn't.
Anyways, the only prediction I have so far if for Fuuma, I predict one of either two endings for him. One, that Kamui will fail to reach Fuuma's old self and will be forced to kill him, thus saving humanity. Or two, Kamui will reach Fuuma, thus returning him to his old self, but the absolute horror of what he has done (killed his sister, maybe killed other people too) will cause him to kill himself, thus saving humanity. Either way I don't see a very pleasant ending for this boy.