Did it get renewed for season 9? I haven't heard yet.... I know they were kicking around the idea of a full length movie to wrap everything up at one time.
Seems like 10 seasons have been the max for my favorite shows. Stargate, yeah they followed it up with some spin-offs but it was never the same after Jack left. I don't think they could ever replace either of those two brothers in supernatural. If they do decide to end it which I hope they don't for at least a few more years they definitely have to have a movie.