I'm assuming that his calluses will be gone, or all but gone, and that as a result he'll be missing/screwing up chords that should be easily held. If he keeps trying to play when he realizes he can't do it right, is it completely off to assume that his fingertips may end up bloodied? (The guitar is an acoustic and has steel strings, not nylon.) If he'd find himself completely unable to play, unable to even attempt to keep playing after a few attempts at chords, that'll work too; the scene is meant as an illustration of how pathetically screwed up this boy's become.
Terms googled: "guitar calluses" (which brought info on why and how you should build them up, but nothing else), "loss of guitar calluses" (absolutely useless for my purposes), "guitar callus loss" (see previous term)
Thanks in advance!