ROFL can you imagine the uproar in fandom if they would actually try to replace Dean with Ruby or Jo for that matter. *g* Kripke would receive homicidal letters in spades and would need to hide for the rest of his life. Apart from the fact that both actors won't get tired to stress how much they love their roles, I can't really see them working on the show without the other. This is the Sam'n'Dean show, we know it, the writers and producers know it, the actors know it. :)

True, they wouldn't actually need to show hell, still I can't imagine they would dare to shoot a couple of episodes with Dean gone. *g* People already complain if one of the boys isn't featured in one episode enough. SN fans are a picky lot. :D