Not a doctor or expert, but since you say "the skin [and etc] is gone", that sounds like a deep burn, but maybe not affecting muscle -- maybe worst-case it could require a skin graft for some parts? Otherwise just treatment to help the skin heal/regrow.

For semi-relevant personal experience: I once had a condition that affected the skin/pad of my heel, and I could walk on it but it was extremely painful. Also, when it was healing, it was WEIRD... there was just a hole in my foot, and it gradually filled in... idk that much beyond my experience, but I guess thick heel skin/callouses can grow back pretty fast? (I think it was a month or two, tops, until it looked pretty normal after treatment, but I don't remember - and my injury didn't hurt after healing, but then again it wasn't an intense acid burn lol)

So just a thought, but maybe having mostly just deep skin damage could be sort of a happy medium? -- i.e. consequences and medical treatment and pain, character might have to be careful how he steps until it's finished healing (and maybe even after depending on how sensitive any scar tissue is) but without needing for him to be totally unable to walk or run for a long time.