Xion is staying, no question about it. She has nowhere to go, really wants to find out how they managed to bring her back in, when there shouldn't have been anything to bring back.

... and once she finds out the Doctor is staying, too, she'll be especially happy. ♥♥♥

How are we going to do things with those who stay? Is there going to be a private game during the summer, or is it going to be handwaved/etc?

I say definitely yes to Christmas and pre-season events! As for things I'd like to see... Moar fighting, maybe? :|a So that I can use Xion's battle icons the characters who can combat get to be badasses. Maybe the event can be set up where the characters who can't combat also get to be badasses behind the scenes. =w=