Oh come ON!
Don't tell me any of you are fooled by the whole Dean can't be saved. It's obviously building to some great conflict with this demon that's on the rise, who was mentioned last episode and what are the odds he has the contract on dean? kill him/make deal/give ultimatum and dean is free.
If either leads wanted to leave they would end the show because
1)the shows ratings are just about okay for the CW on a thursday night, where anything else would get killed.
2) more importantly this isn't heroes or lost with a cast of multiple main charecters it has two main charecters and for season 1 & 2 the only two recurring charecters. you can't kill them off or the show ends.
There dad got killed off in an attempt to make the show both better and darker by isolating them even further and it worked brilliantly as last season it went from very good to being a a outstanding show.
Thankfully they have decided to keep the dark feel to the show and so the whole dean is dieing storyline is a great way to go with that.
Great episode btw which makes 3 in a row now all these shows that decline year after year should take a look at what supernatural is doing as it just goes from strength to strength.