So I was showering and a thought occurred to me.
Daddy Winchester is and will always be a hunter and whilst I appreciate the sentiment of "Dean's my son, I'll sell my soul to the devil to save him." The cynic in me can't help but wonder if this is part of a bigger plan.
Let's take a look at it like this, John has been hunting this demon since Dean was four and he's never stopped and nothing's been more important to him than killing the demon.
Take for example when Sam's driving the car, dad goes on to say how nothing is more important than killing the demon. Now forgive me if I'm wrong but those words aren't just flung around lightly. John Winchester says what he means, nothing more and nothing less.
Maybe he did get a shock of his life when he saw Dean in a coma and realised what hunting the demon had cost but again, I doubt it however. John's a strategist, a very smart man and he's a soldier. He knows that there will always be casualties of war and whether or not he wants to admit to it, his boy happened to be a casualty of the war they've been fighting.
I think that John did what he did with ulterior motives, the primary being to save Dean but the others involving the vendetta he has against the demon. If you think about it, John won't have gone to a peaceful ever after because of his unfinished business and you can exist after death. Being a ghost places him more in the demon's world than it does the actual physical reality so I'm thinking and I'm hoping that some sort of storyline is going to happen around the decision that John made in that hospital.
Or this could just be the ramblings of a tired insane fan, who knows?