Wounds/broken bones are healed through exchanging power, so it's obvious to me that they exchanged power with someone else or between themselves (when they healed a bit and gathered energy).
in the epilogue hulie told xianling that he is an excellent spellcaster even with one hand so i think he can't use his hand again
From what I understood in that part was when Lifang recalled his memories and powers it also flowed back to his friends and healed them same with the people with the critical condition to show signs of healing.
BUt oh well who knows ¯_(ツ)_/¯
There's something that's bothering me no matter how many times I read this manga. In the end, when xianling overused his power and he's hurt his arm, hulei point this out to long. Same with nasha and her leg. Does that mean they can't use arm and leg anymore? I saw that xianling never moved his right arm in the epilogue so...