We had an older homeless woman here in town who refused ANY offer of help for years and years, she eventually declined to the point where she met the criteria for involuntary placement into an assisted living facility. She was angry and miserable for the first month but eventually realized that the comforts of having good food and a clean warm bed were kinda nice, she started to enjoy her new place and remained there happily until she passed away three years later. Hopefully your friend will be able to find such a placement when he's no longer judged capable of self-care.