Can they choose anywhere on the work / life continuum? Maybe sometimes. Can they just go do something else? It's not always that simple.
For the record, I am currently self-employed again after a five-year stint in big tech. Prior to that I worked for myself for more than a decade. I’ve seen this issue from both sides, and I definitely wouldn’t say most entrepreneurs can pick anywhere on the work/life balance continuum. But again, we’re not talking about most entrepreneurs, or even really about entrepreneurs at all. We’re talking about people who have reached financial independence, specifically your relative. All of this would still be true if they were an employee who had enough money to stop working tomorrow.