What if Castiel had taken a different vessel?

Apparently Supernatural was real, which was presumably why Gabriel was bleeding out onto Richard’s floor. (In which the actors of Supernatural find that reality is stranger and more disturbing than they previously believed, even counting Misha, and an injured archangel discovers that his universe is the subject of a TV show.)

Gabriel has a way out, if he can just get the gods on his side.

Two hundred years ago the Winchesters stopped the apocalypse. Now, instead of getting into fights and running amok, eighteen year old Jim Kirk goes to live with his Auntie Sam and learns the family business. Four years later, an angel shows up.

Sam smiles, bright and luminous. "An angel's Grace isn't just power, Dean. It's a part of their soul." An AU 'verse that takes place after episode 5.22.

Looking at the contemplative expression on Lucifer's face, Sam thinks that this has the potential to be either very bad, or completely awesome. Two humans and two archangels in the Cage.