Oh I feel so bad for him! I don't think I've ever had it that bad, but even to the extent that I've had it, it's bad. And yep, not exercising just makes it worse.
If chiro helped him, it probably means that the way his bones go together in his pelvis naturally wants to "squeeze" the nerve, and chiro helps to ease them away. Since this is how his body has been for probably his whole life, it's probable it would take quite awhile to get it to "hold", and it's possible it never would.
Just as an example of what I've gone through...for whatever reason, 10-15 years ago, my shoulder started acting up big-time. It's where I hold my stress, I get a really tight shoulder when nervous, sad, mad, etc. And it would just hurt all the time. I was in practice, and my shoulder was driving me mad, and I knew I was having different levels of feeling in my left hand compared to my right, because it was messing up the way the nerves in my hand were talking to my body (and the way my body was talking to my hand). It's one of the many reasons I gave up practicing. If I'd ever found the money to get disability insurance for myself, I very likely would have waited longer, gotten a diagnosis, and started collecting on that insurance, that's how bad it was getting.
I've never had my chiro-friends look at it, mainly b/c I usually go to the kinds that don't look elsewhere on the spine. Then I found this awesome guy who is very grounded but also floaty; he talks about energies, but also takes personal injury cases. He has a great monthly family plan, but will bill insurance if you want to do that instead. etc. And he's MORE than happy to go beyond the spine. Last week, he did some tiny little thing to my shoulder (ouch ouch ouch, but only momentarily), and for a few days it really felt better. Even now, though it feels almost back to the same, it's still a bit different. I would bet it's going to be at least a year until it really starts feeling good and I bet I'll have to have it checked out regularly. For whatever reason, my body wants to hold my shoulder (which affects ribs, clavicle, shoulder blade (and muscles around it all), and also the vertebrae nearby) in a very funky fashion, and I don't expect it to keep itself in proper place for a long time.
So if it worked, and if he liked it, and if you can find someone really good and trustworthy and someone who has a reasonable monthly plan (if your insurance doesn't cover all the visits you want)...and if he can be comfortable going again and again (since it helps), he wouldn't be the only one going often for something that's been chronic for what seems to be a long time.