Zuck could take the rest of his life off work. And when he's an old man he will wish that he had. But in the mean time the share holders can benefit from his keen.
He could have done that when he was 19 years old. Obviously....OBVIOUSLY.... Zuck, and Facebook, are what they are because he doesn't agree with your views on his life.
How do you know he wouldn't regret stopping work now when he's an old man? You have absolutely no idea. But we can take an educated guess by the motivations and choices he's shown in the past. Which were, to keep working and building his company. Because he probably enjoys it.
My grandfather grew up dirt poor. He built a small real estate business on his own, and continues to come to work every day and he's in his 90's. If he was forced to "take the rest of his life off" not just 20 years ago, but even now, he would without question be less happy as result. He enjoys working. Many people do. Especially those who are founders of businesses.
When people get old they don't have much in their life other than their family and work, and many workoholics have only their work, case in point Warren Buffet, that's not proof that they would rather not do anything else. Or would've lived their lives differently if they had the chance, and many of them might be too proud to admit it at this point considering that they will soon be gone. It's just that work is the only thing left that makes them feel useful, wanted, and provides some sense of purpose in their lives. They have been so busy in work they don't know what else to do... nor is their body and brain capable of doing much more than what it has done most of its life.
Many rich business people completely quit business and instead do philanthropy, case in point Bill Gates... Zuck's role model? Facebook is not something positive in the lens of history. It's just a big money maker. Maybe it will still be relevant in 20 years, but eventually it will be seen for what it is... as if it's not already. And all that will be left is the money, of which Zuck has more than enough to do much more worthwhile things with his life. Like perhaps philanthropy. Maybe he can really solve some problems before he dies in 40-50 or so years. Of which maybe the 10-20 next ones will be his prime.
This guy once gave at talk at my university where he said he regretted not doing a lot of things because he was working and now he was too old to do them because of his health.
He sounds like someone who would give a great talk. I can see that happening for sure. I've devoted my life to a lot less before realizing there was more out there. These people put so much time into their work there's little left for a broad life - unless you make some clear boundaries like Mark is doing now. Maybe this will be a one time thing and, as you suggest, he may regret not making more time for other areas of his life. Maybe he'll manage to carve out more time for himself.
I don't buy regret. From what I've read so far, people who worked too much regret not doing things with family, etc. and people who lived bog-standard GenPop family life regret that their life had no meaning. So I guess death is just one big paradox of choice.