How to spend the rest of his days freed now from the responsibility of earning a living and raising a family? Short of a major disaster in the national economy he has quite enough to pay his bills and meet his needs and even more surely provide for his wants till kingdom come - his kingdom at least. (He had made due provision for his darling spouse should she be fortunate or unfortunate, about that you must ask her, enough to survive me.)
In the meantime, what should he do? Become a spectator, or a passenger, seek to be entertained, amused, or travel the world and see its far-flung beauties? Or join in the human evasion through social or political activity?
Something odd here. If he takes up a hobby or pastime, or joins a club that gets him out and meeting people, it will be perceived by others as a personal achievement, a mark of sanity. If he stays in and devotes time and thought to solving the riddle of existence, and perhaps becoming disillusioned and discouraged by what he finds, he will be seen as escaping from reality - the very reality he is trying to understand.