I failed to save the Tieflings. I'm not even sure what I did wrong. The quest just failed.
I honestly feel pretty bad about it. But I don't know how old of a save I'd need to load to fix it.
So...they're just gone in this playthrough, I guess.
My next playthrough was going to be a dark urge playthrough; but now I think it might be a Save The Tieflings run.