I also think it's going to end violently. I have come to expect one of the brothers to kill the other. Probably Dean having to kill Sam because he finally goes dark side. It has to end violently, there is no way it can have a mushy ending. Please not a mushy ending!

But like you said, Kripke does do the unexpected. Not many thought Dean would actually go to hell but he did. So whatever happens it'll be a surprise and it will be good!