Sayori, of course, will bring Ango another cookie and check in with him emotionally. If he seems to be having a hard time, she will try everything in her repertoire of (metaphorical) bottles to help; comforting minor illusions, discussing Caleb Cleveland, hugs, a Bardic Inspiration if that wouldn't cost a roll.

Once he seems to be doing okay, though, either after any attempts to comfort him or without needing them in the first place, she will ask if he's ready to get down to brass tacks and do some detecting about this scary place. Starting with anything he might remember from his readings on the history and theory of magic, or that whole encyclopedia he read, that might tell them what kind of magic could kill a tree that's supposed to survive the end of the world.

EDIT: Also, would Angus be willing to help with some RESEARCH? It seems like it would be right up his alley!