Yep, I haz a theory. Keep in mind that I'm usually wrong, but this popped into my head after watching the videos.
So Sam is off to learn from Balthazar how to keep his soul out of his body which means getting the blood of his father, or father-like figure. Which means Bobby. Eeep! Meanwhile, Dean has died (again!) in order to make a deal with Death to get Sam's soul from the cage. From the looks of the promo, Sam's about to kill Bobby (Noooooooo!!!!).
So here's my theory...vague as it is....Dean's gonna come through, fulfill being Death for a day, and get Sam's soul back....just in the nick of time before Sam plunges that knife into Bobby. Insert much angst, pain, & remorse from Sam, Bobby lives, and Dean rushes back to Sam for a comforting brother hug.
Ok, maybe that last part is more wishful thinking on my part, but you gotta admit they're overdue for a real hug! ;)
What do you think?