Thanks for the advice, I'll remove the bone today. Necrosis is like rotting/infection right? It just looks like a stump! No drainage or anything, last week he did bleed just a little though, nothing huge. I probably won't be able to get him x-rayed though.
I couldn't do anything about the arm, I don't think he would tolerate any kind of splint and even if I tried to splint it he would probably just get more stressed.