Basically, I have an AU version of Hojo from Final Fantasy VII (set post FF7, Jenova is not a factor.) Technology / magic levels are comparable with the game. Hojo's arm, mutated and infected with Jenova cells, is now rejecting said cells and attempting to return to a more normal state. (Things may have been made worse through some botched attempts to use healing magic which could be attempting to shift bones / muscles back into a more normal placement.) The Jenova cells may be dying, which could result in gangrene. Hojo has a working nervous system in the arm, some muscular control, and some of his original muscle mass / bone structure.
Hojo has been arrested by a group, and their doctor is told to keep Hojo alive, and if possible to save the arm. It's quite likely Hojo is not in good health at the time due to said infection and the inability to get good medical care for it. The doctor is hurried, but has just about any medical option available. He is not an expert in medicine, but he has familiarity with the trade. He has up to date medical files for Hojo (so things like allergies, etc. are not a concern.)
I'm theorizing that the doctor would probably want to try to get Hojo on antibiotics as soon as possible through an IV, and possibly to use surgery to remove any material with gangrene. I'm assuming that Hojo'd probably need to be isolated to reduce the chance of secondary infections due to a strained immune system. The poor health factor would probably equate to another IV for hydration / caloric value.
1) Does this scenario sound plausible if the end result is a very weak and ill Hojo with a sore and slowly healing arm?
2) Due to the rushed nature of the doctor's work, I assume that a visual inspection of the arm is sufficient? Are there any other tests that he should probably do? (White blood cell counts, maybe?)
3) Assuming Hojo has mild pneumonia, is underweight, and has said bad arm, does it sound probable that Hojo would keep said arm, or survive? If not, how could I tip the odds more in his favor? Some manner of a lung ailment would be thematically useful, but if it's going to kill him, it obviously can't happen. If it's a case of the doctor strongly suggesting amputation, that's also fine, since it's good material for arguments.