We know that there are two endings to the Yozora battle. Either Sora wins and Yozora fades away or Yozora wins and Sora goes into crystal stasis like a l'Cie or something.
We know in the game's data that one ending is labeled the "true" ending, and I am hearing rumors that the novel goes with the bad ending with Sora being crystalized.
This got me thinking. With the existence of worldlines in the series, what if both endings are canon?
What if because both endings are canon, we will follow both storylines until they converge. If this is the case, what if worked like this:
Kairi is sleep and finds her way to Sora in the worldline where he wins.
Riku dreams and finds himself in the worldline where Sora loses.
Both experience their unique stories with finding/saving Sora.