I was once a burned out surgical sales rep with 3 little kids and an angry wife. (Because of all my time spent working and away from home)
It was time for a change. I wanted to make a difference in the world and do something that I could be passionate about. I started a venom lab and now I extract venom from snakes and process it for pharma manufacturing. (That sounds glamorous, but I spend much of my time scooping snake poop) I didn't pay myself a penny for the first 3 years and then it took me another 3 years of making a very modest pay till finally I'm now where I can make similar pay to what I made as a medical sales guy.

The thing that makes this comparable to what you are saying; is that there is the perception that what I do saves lives, and therefore I make a difference in the world. What I've realized, is that while society puts vocations that "save lives" on a pedestal, they've gotten it all wrong. The law of averages suggests that if you save 100 lives, there will be some really good people you saved and some not so good people as well. I know a story of a serial killer who's life was saved in a hospital and then he went on to kill lots more people. That doesn't mean we shouldn't save lives. It just means that we are delaying the inevitable and while doing so, the world continues to revolve at the very same pace that it did before with the same amount of good and bad going on. The great news about all this is that ANYONE can make a true difference in the world by being kind to everyone they encounter and they don't have to be an MD.

What he should ask himself is this: would working with patients and nurses all day put a smile on his face. Would that work energize him so that he felt like he was fulfilling his purpose in life? Would that allow him to be a better father and husband? Is the time he has to spend with his kids valuable? Since my career change, I am 100% more happy and it wasn't because of more money or status. It's because I 100% enjoy my work and my family is 100% more happy. I spend much more time with them now. That's worth all the money in the world. If his wife would be really happy with his new career choice, then he should go for it. If she doesn't like the sound of it, I would avoid it at all costs. If your soul is yearning for a purpose and you feel like you've found that purpose that is a big deal.