And what about Michael the arch angel? They can bring him back having the need for Sam and Dean to finally fight to the death as vessels for lucifer and Michael this time ending it in a titanic battle. Ideas ideas.

It is a perfect ending. Since the beginning of this show though there is one unanswered question still unanswered in current season 11. Where is god? I think when God finally shows up and something totally epic takes place they can end it. They would have to.