Long term consequences, like death or health related problems, don't seem to deter addicts. I wouldn't count on the health issues to keep him from using. I don't have any experience with nitrous.
If it were me, and he was living in my home, I would insist on a medical evaluation because I would not want to have a drug-realted health emergency to deal with. That's just me.
Hopefully someone with more experience will come along.
HUGS
Molly