Thought I'd let you know how it turned out. As usual, Carnival came through for us. I canceled Dad's cruise and they deducted the increase in the other two, non-military fares from his paid fare and the difference is what I will apply for to the insurance company.
Not nearly as much trouble as I expected and my PVP was very helpful. We will cruise without Dad/Grampa, but we will have a wonderful time and share our memories with him!