I agree that, in all likelihood, he's dead. I don't think however, that the U.S. will ever make the claim unless they have tangible evidence to prove it. If they did claim he was dead, and OBL somehow made it evident to the otherwise, that would be a big pie in the face to the Administration.
But then again, if he's alive, he is too much of a delusional egomaniac to NOT come out and "stick his tongue out" to rub it in.
I think Tora Bora, or egress from there, did him in.
If he's dead, that's a HUGE step in the right direction. Remember that he's not JUST al-Qaeda's spiritual leader but also their major financier and mastermind. With him out of the picture, you've decapitated the biggest part of the operation. Not the end of the war, but a huge battle victory IMO.