User blog comment:Touchinos/Supernatural Season 15: Endgame/@comment-1031724-20190327051830

Two theories on how Season 14 will end.

Both involve Lucifer forcing Cosmic Entity to revive him, and possessing Nick again. He has Jack's grace, but Jack has his power back through Michael's grace. When Lucifer returns, it's clear only Jack can defeat him. But, both my theories go that Jack will lose this fight, leading to one of two desperate decisions to end his threats for good this time.

The first is for him to combine his archnephilim powers with what remains of his soul to destroy Lucifer, and without any of his soul left, becomes the next main villain. (An issue with this is he'd be too powerful to stop now)

The second, as I mentioned below, is Jack releasing the Shedim, figuring only they could defeat him, which he likely never would have done if he had all his soul. They kill Lucifer and become the villains of Season 15.

Or, maybe Cosmic Entity can't revive archangels and leaves the Empty to take out his frustration on Earth or something. So many possibilities but I don't know if I can be satisfied anymore.