Heya Monkey, Sorry to hear about this
Well at this point u gotta question his heart, there is nothing u personally can do. You could get a forklift n forcefully haul him to the gym but u cannot alter his mindset and attitude toward training.
If he wants to box, if he wants to fight competitively he's gotta understand it's gonna hurt and to be a fighter uv gotta jus fire back regardless. not mope about licking ur wounds. Thats no just applied to the pro boxing scene, thats for the amateurs, semi pros, kick boxing muay thai, everythin.
If he decides to come back u gotta test his will, determine whether he's got the grit for the business.