That nerve can be WAY less than 100% and he won't need the brace. In 9 months after my nerve was damaged I had 100% use. However, 11 years later I can still feel a little bitty bit of deadness remaining. No biggie. He may never have 100% feeling back, so what it doesn't matter.
As long as he has enough feeling to move his foot and to know where it is at all times I think he'll be functionally 100%. What we haven't spoken about is that the nerve can start going dead again in the future! If scar tissue like gristle forms at the healing area in his knee, that can constrict the nerve and it will start dying again. No big deal. The doc goes in and cleans the gristle out and it is fixed .