They really should have let the whole thing die. The only thing I hope for in the future would be a team up with Ackles, Padalecki, and Kripke making a new show some years from now. Retcon seasons 6-15 and pick the show up 20 years after the events from Season 5 (which aired in 2010, so 8 more years from now).

I think you could literally have the clichéd sequel that repeats the story from the original but with some changes (like 22 Jump Street) and people would like it. These spinoffs that they do don't work well because people liked the aspect of these two guys hunting monsters. Figure out how to get that going again and you'd have a good show.

Dean is in his early 50's with a family when the same thing that happened to his dad happens to him. He then has to get back into the life while taking care of his kids and basically becomes what his dad was, someone mercilessly hunting the demon that murdered his wife. Turns out the demon that killed his wife is Sam (or someone with Sam's body), returned from Hell. Cue a season or two or good ole Supernatural. Maybe Dean goes on a hunting trip and doesn't come home for a while and his kids have to go after him, leading to some Monster of the Week type episodes. Hit the same story beats they did in the original. Make it a show about people searching the unknown, trying to hunt things and save people. It works best with a smaller cast.