Hello again @bri3sd He is three months out now so I would expect this would get a little better by now, certainly not fully recovered by any means. Gargle with warm salt water several times a day is the primary route most often recommended and for me, that worked. There is also a solution known as "Magic Mouthwash" which has I believe contains Lydocaine along with antifungals and other healing ingredients. This is by prescription only.
Another solution is Red Light therapy, which using infrared light from a wand in the throat has worked well for many. I'm often a skeptic for things like this but I have known of excellent results from this, even from one purchased by mail order.
Go with the warm salt water today, now, right away. Then ask his GP or oncologist for Magic Mouthwash if you think that will help.
It hurt for me to swallow for at least a year. Roughly fifty muscles are involved in the swallowing process, many of them damaged by the radiation. It takes time. I often exercised these muscles by sipping ice water or hot water (coffee/tea/broth), whichever felt best at the time. Doc said likely the salt in the broth was what helped the most. Courage. "Razor Blades" That's an apt description. I agree.