Unfortunately I don't know enough about such injuries in terms of current medicine, let alone historically, to come up with something I'm comfortable writing at this point.
Searched: 19th century gunshot wounds, 19th century medicine, Napoleonic Wars, battlefield surgery, Peninsular Wars, casualties, injuries, all in different and varying combinations on google, googlebooks, googlescholar, a local (county and community college) library's online databases as well as the catalogues. Most of the information I've found is on the American Civil War...
Edit: I forgot to make it clear that he is an officer, if that makes any difference in terms of granting leave etc.
*as much as I would like to avoid amputation it really is ok if that's the only feasible option. So if you've got a scenario that works perfectly and includes him losing a limb I'd like to hear it at least.