my experience tells me that he has about five years just going with the doctors or he can devote himself to a lifestyle change and that basically is doing just about everything on curezone till he finds his high water mark. it is extremely hard for those over 50 to decide to change. if he makes the decision and seeks change earnestly instead of constantly trying to dodge it, he could see his 100th birthday, and that without assisted living. its entirely up to him.
ask him this - would he give up all cake until he could eat a piece of his 100th birthday cake? if not, he doesnt want to live and you cant make him.
the first thing he must do - abandon doctors completely.