If you can keep him eating, protected from flies and the other chickens or critters attacking/pecking him, and he keeps pooping, then I'd keep treating him. The Vetrycin was great and I sprayed it as often as I could, at least 3-4 times a day in the beginning and put the neosporin on her when the wound was so bad - towards the end I backed off but did try to keep it clean. Don't use peroxide - it's tough on the tissues, despite that being what was the norm in the old days. I did make my own saline solution when I needed to clean in the beginning and to soften the scab, then always put on the Vetrycin when I was finished then the neosporin.
Good luck!!! They are amazingly resilient and if you persist and help you may be successful.