(Sorry, a bit more)
Without magic
A skilled surgeon would do only a % of damage- cutting into the wound-that they rolled over 100 as a neg modifier to extra hits; or something...
Also, w/o magic, the penalty may be permanent!
Again the over 100 roll could reduce this penalty by the % over. If you have a -30 on that arm from now on, the skill or luck of the surgeon could reduce it to -20, -10...
There may always be a penalty...
Which could be helped w/ rehabilitation!
Of course this will be beyond most "healers" in this setting, but could be lost arts, hundred(s) year old elves... Probably only in cities...
I'm thinking of the M*A*S*H TV show. They were better than good. For the time, they were the absolute best.
Just my thoughts on the matter.