I'm looking for a fic I read a while ago, what I remember is it's an au of the apocalypse. Team free will along with Gabriel decide the only chance they have to beat Lucifer is for Dean to let Cas use his body as a vessel, but when they're fighting Lucifer he rips Cas out of Dean but is killed by Gabriel inside of Sam. Afterwards Dean is super depressed and almost comatose for awhile, but manages to start pulling himself together. At one point Dean stumbles across Cas's empty vessel and breaks down. Cas comes back to life at the end. The pairings were destiel and possibly sabriel. I'm pretty sure I read it on ao3 and it's been driving me nuts hopefully someone can help.