RE: Do disposable diapers "go bad/expire?"
First things first: I am so, so sorry for your loss. I will be thinking healing thoughts for you and sending prayer (if you don't mind).
Secondly: I work for the makers of Pampers/Luvs. I've heard that question before in the context of diapers sitting on the store shelves, and generally the answer is no, they will not go bad. In your case, I would store them in a cool dry place if you choose to keep them. Since there is gel that absorbs the urine present in the diaper, I would imagine that since the bags are open there's a possibility they could absorb a small amount of moisture out of the air if it were excessively humid-- no science to back me up, just a gut feel.
Again, thinking healing thoughts for you.
Edited to clarify.
Mommy to DS (9/03) and DD (5/08)