I had a two stage revision in 2009 following an infection in my left knee. At the time the surgery and subsequent recovery was long, frustrating and at times painful, but 5 years on I am living a normal life and can do almost everything that I want to. I haven't yet mastered kneeling, and getting up and down from the floor elegantly, but that may be more to do with the number of surgeries I have had on my left knee rather than because of the infection.
All the best to your friend. Do keep us posted on his progress. Linda x