So, to me what to do would be simple. Sure, he just won the part of life dealing with having funds to live a life... but is that all there is to life?
If you are one to have a religion... I am sure there is plenty to learn there
I assume he still "thirsts for knowledge"? I know money wouldn't automatically teach me everything about the cosmos.
Isolation? why is he isolating himself? I kinda question the girl that left him because she wanted a more normal person. It sounded like she was concerned about his life style, not his potential life style. That to me doesn't sound like a choice of money, but a conscious choice of living a specific lifestyle.
Now, one challenge I could see, he started a company, grew it well, and sold it for a bucket of money. If that was his main motivation in life (work life balance much?) he will need to re-direct his motivation. That is if he looks at it as winning that part of life. Then again I do know entrepreneurs (dealing with much smaller amounts of money) that enjoy building up the company (restaurant/etc), just to sell and start up another.
I could imagine many different things I would do, free time to try my hand and research/higher degrees. Also, all my hobbies... I could spend plenty of time there. and since many of those are hobbies that can include people (its not like im just sitting there painting warhammer 40k figures all day long) I would still socialize with others. Frankly I wouldn't move far from where I am now, and would retain my same friends (I am sure they would get to receive some of my fortunate luck too). Honestly, I think I would still want to pursue some work, whether its "real" work or volunteer type work, I wouldn't want to turn to mush.