Your theories are essentially my theories. Except mine also include the bloody death of Ruby.

And they gon' die, son. They have made many comments about "it's gunna end bloody" and all that. Kripke wants them to go out like Butch and Sundance. Jared wants it, too. Jensen's like, "Whatever, I'll do what they tell me." It's going to end with Sam and Dean vs. the World, going out in a big fight. Which will mean I won't be able to watch the show for like 2 years lol.