So I see most people chopped off Lee's arm based on the statistics. I personally didn't. The fact he had already collapsed to me suggested that the virus/infection/whatever had already spread past his arm into his central nervous system. Cutting him arm off at that point would only render him less able to function and possibly kill him from pain/blood loss.
Do things play out a lot differently if you DO chop it off? I'm guessing Lee still dies either way.