See, I think Sora wouldn’t change too much by changing Kairi’s death. By going back in time to save her, all he has to do is just stop Xemnas from taking her away. From there events would mostly unfold the same way mostly except Kairi and Sora would have a moment where they reinforce their promise with Oathkeeper, and then Sora would go against Xehanort.
Xehanort used Kairi as “motivation” before but now that Sora knows how things will go, I imagine he’s willingly clash against Xehanort.
It feels like a cheap rewrite of an otherwise rather emotionally impactful final segment (everything from the start of Scala to Xehanort and Eraqus dying was actually really solid and I wouldn’t want to see them change a thing about it), but I think they can change Kairi’s fate without changing the whole ending and its own climax.
Perhaps they could use that to expand on Xehanort’s past with Scala, too, if they are inclined to do so to add a bit more story depth to the Scala segment.
There are two DLCs in Re:MIND
Limit Cut and Secret Episode.
Limit Cut is what we saw: an expansion on the existing story.
Secret Episode will introduce new story stuff.