Bramps, Adele DID sing live.
They (everyone MINUS Adele) were in the studio practicing and re-orchestrating everything to shorten the song for Oscar appropriate length.
The father of a good friend of mine did the orchestration of Skyfall and said that Adele (and Paul) were the most incredibly humble, kind, and enjoyable and down to earth people to work with. And he has QUITE a resume himself and has worked with a ton of people on a ton of things you’d recognize.
I like Adele’s music but that performance was weak.