I can't really share your hope, because I have an automatic gigantic sadface reaction to the suggestion of one of them dying no matter what the circumstances. But I'll admit that it would be sort of awesome to have a ghost hunting other ghosts. And Dean would have to get over his general 'SPIRITS BAD' attitude if he's working alongside his brother's spirit, which could be interesting. And it would make using salt more difficult if Sam could be repelled by it as well.