So this last episode of Supernatural, Criss Angel is a Douchebag, continues to confirm my suspicions of where the season is headed.
Everything I see, including this last episode we just saw, points to Sam falling at the end of the season.
Not to mention, the writers take the horror show aspect of the show very seriously. All of the seasons have ended really badly for the characters - and in Season 3 they initiated a wonderful pattern of giving the audience exactly what they promised all along and having the final themes echo all along the season. Tightly woven foreshadowing.
So, we've already been told in so many words that Dean won't be able to stop what's coming and that he shouldn't blame himself for it because what ends up happening will be destiny.
So, I think Dean is going to end up feeling deep anger at Heaven/the Angels/God at what he will feel is his manipulation.
IOW, the Powers in Heaven left him rotting in Hell long enough so that - through the process described in this post - he got far enough along to his own permanent damnation that, upon being released, he would have an insatiable desire to rescue people - a desire which can only be sated by saving the world from turning into Hell on earth. That's the only way he can get his sense of self and any sense of self worth back again.
In other words, Heaven set him up to be a counterweight to Sam.
And I think that Uriel's trick to make Dean betray either his brother or Anna, knowing he'd choose his brother, is going to be the template for the final decision he has to make. He'll either be able to save Sam from getting all demonified and going to hell, or reigning in Hell or something like that, or he'll be able to save the world - but he won't be able to do both.
In the season 2 finale we saw Dean explicitly turn away from shutting the gates of hell to look for the YED so he could get him. This time, I think he'll have to do the opposite - save the world and leave Sam - because this time he knows explicitly what Hell on earth means - really means -and he's not going to let that happen on his watch. Not if he can prevent it. That's going to be a more important pledge than keeping his brother safe - which was his job, the thing he was conditioned to do, since he was 5 years old.
So he's going to have a choice beween the two most important things for him - saving the world and himself thereby or saving Sam. And this time, I believe he'll choose the world. Just like in the episode we saw tonight, the old guy made the right, moral decision but ended up killing his friend and being alone and hating himself for it. That is the position that Dean is going to end up in, I think with tons of questions and man pain about whether he made the right choice.
As for Sam, it would be cool if he went darkside by killing Lilith who was in the middle of killing Dean, since Dean is his weakness and he would easily use his powers to the fullest in order to prevent it. It would also make Dean's pain so much more intense that his brother went dark saving him and he didn't reciprocate. The one thing that seems clear to me is that after Dean's confession of what happened to him in hell, Sam is not going to let Dean go back to hell. Also, this night's episode shows how much pain Sam still is in from being left alone when Dean went to hell, not just once, but twice - in Mystery Spot and in No Rest for the Wicked. A pain that has gotten shunted aside, because Dean's issues were so much more weighty and Sam has never yet confessed to Dean or to anyone what happened in Mystery Spot and how long it lasted for him and how much pain he was in - it's an experience that seems to have changed him a great deal.
It would be a nice touch in terms of foreshadowing the ending, if towards the end, Sam offers Dean immortality or power or somesuch, like the immortal "brother" offered to his two friends in tonight's episode.