I think Jimmy is still alive in there, because Castiel told him something along the lines of "You'll never age, you'll never die, if you think one year was hard - this could be thousands..."

So, yes, I think Jimmy is still alive in there, but it sounds like he may never get control of his own body again. He'll forever be a passenger.

These next two episodes are going to kill me. Sam is gone. Dean's completely destroyed...and I remember thinking last year that Dean going to hell was the absolute worse thing they could put him through...how naive I was!