JJ - You say: "Fundamentally, he enjoys hitting a ball around as well as he can with good people."
"He does play from the 6,000 yard tees, as the senior group he plays with at his current club all want to play from there, which is great. (They play Stableford format, and quickly.) He's beyond playing formal tournament golf, for a variety of reasons, but getting out once or twice a week and hitting the ball around will do him a world of good."
Your father's talking about quitting. Why? From what you've said, I don't understand the reasons, and it seems to me you (we) need to understand the reasons to know what to suggest.
My situation. I'll turn 75 in a couple of weeks. I started playing when I was about 50. Lowest handicap ever, 14. Now mid-20s (and rising). With recent surgery I'm out for at least 6 months. It's killing me. Fortunately, I can still go to the club Tue. and Thurs. afternoons to meet "my group" of seniors when they finish and settle bets in the bar.
For me, it is all about the game against the others. Handicap, posted score, e.g., 98, are meaningless to my enjoyment. The good stuff. Winning (or trying to), hitting an occasional really good shot or making a good putt (I do not concern myself with bad shots or poor putts), socializing through golf with friends, fresh air and exercise. I don't see how you can beat it. From my personal experience, the guys who have the hardest time with failing skills are those who once were really, really good at it. Guys who were scratch or near, now late 70s and 80s (age) and are 20+ handicappers. Some of them measure success differently, against their former selves, and that's a problem for them.