Easy, move it back to the Soundstage. But as a temporary thing with a ton of capacity, probably more than the Soundstage, it could be workable. And let's not forget, "How the Grinch Stole Christmas" was also a cartoon too, so it wouldn't be completely out of place, although I acknowledge it would be somewhat of a stretch. Not saying this is what they should do, so to speak, just throwing it out for discussion's sake.
3. What happens to Grinchmas when the time comes when they want to get rid of Theater, or put it to good use?
They have plenty of space behind Seuss for a possible Mt. Crumpit.