I wouldn't aim for a traditional office job with that kind of money, but I'd want to be doing
something. He could go to graduate school, write a novel, start (or at least join) a non-profit.
With a trust fund that can support him indefinitely, he certainly has nothing to lose in taking a job. If it turns out to be a hideous waste of time, he can quit.
One of the intractable unfairnesses of the work world is that those who need or rely on their jobs are destined (all else being equal) to be less successful in their careers, because they can be trapped into a dead-end and because they do have a reason to fear the boss. Your friend, on the other hand, didn't have that problem. He can take a job and, if it turns out to be a waste of his time, quit^ and do something else.
(^ I am not, of course, suggesting that he ought to quit just because a job gets difficult. What I'm saying is that the biggest danger of the career minefield is stagnation and unrecognized toil, in which case one really is wasting one's time in going to work, and your friend had an inexhaustible "get out of jail free" card.)