User blog comment:MrPedroNorris/Gon Condition/@comment-5780397-20151127153009

It is feasible, but also weird. Gon had grown to a point where he could defeat Neferpitou: during their fight, he did not grow anymore, so it is strange that he would so so afterwards. The backlash was probably "just" his body falling to pieces (in a sense, you could compare his weakening to extreme old age). However, he retained his older body while dying, as his size compared to Killua's proves.

"Heal him" could have been too generic. It might have closed Gon's wounds, roused him from the coma and prevented him from dying, but left him with that frail body. I think Killu ahad anticipated it and so had Alluka return Gon to how he was before transforming for this very reason (to give him back his normal body).