I hope everything works out alright, I know how hard these situations are, 2 years ago I had to nurse my father for almost 6 months as brain cancer finally took over and destroyed him. All I can suggest is to talk with him as much as either of you can. I'm sure another man in that weakened state would slip away if they didnt have that will and determination to keep fighting that your loved ones give you. So being there to constantly remind them what theyre fighting for is really all you can do.

Good luck, and stay strong.