Oh Im so sorry to hear that. Shingles is particularly nasty the pain is horrible and now a kidney infection on top - Im not surprised that he has delirium.
Infections, pain, delirium and hospital stays can all progress Alzheimers, so you have got a right cocktail there. It can take up to 6 months for delirium to resolve, so its mostly a wait and see game, but to be honest, in my opinion (which might be wrong) he is unlikely to get back to the level he was before. It might even be that he doesnt improve much at all.
I think you might have to start thinking about possible outcomes - not to depress yourself, but to look honestly at how you would cope, what help you would need and what your lines in the sand are. Then hope you dont need it.