About the sans Fictive: It is, and it’s not even my Fictive. But I’m pretty sure this Sans doesn’t have a home now. He didn’t actually belong in that AU to start with, but it was his home, and the love of his life was there… How can someone think that’s ok to do though?

Unless the AU was created/destroyed by a soulbonder/tulpamancer/someone else deliberately using that AU to call/create fictives from it, then they don’t have any moral obligation to maintain that AU- fiction is fiction, as far as they are concerned. (If they DID create the AU for that specific purpose then destorying it was a Dick Move.)

If you are someone who believes that fictional universes can be created or destroyed by their author saying so, then you have some power in this situation. Write a branch of the AU where circumstances bring everyone back, and everything will be fine.