If the injury is full healed then what is his real goal now. If it's to get back what he had and he's not a lot older then he was he should be able to do it the same way. He can get amazing gains from an AAS stack but GH could help if he's getting older.
If he's healthy and sound other than the missing limb then he's in the same boat as anyone else.
Regardless of what he decides to do GH can only help things if he can afford it and is in his 30s at least. Getting the muscle and conditioning back that he had will probably happen as long as he repeats what worked before (hard work, food, rest and AAS).
Very wordy and a little hard to follow but -
http://www.clinchem.org/cgi/content/full/43/6/950
One I like 'cause I have a bad liver - is
http://endo.endojournals.org/cgi/content/short/en.2004-0655v1
I know your friend is not a newt but this is a good article regardless-
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3199095&dopt=Abstract
and it gave these rats wood -
Conclusions: Our results show that GH injection significantly enhances the regeneration of NOS-containing fibers in the dorsal and intracavernosal nerves after unilateral cavernous nerve injury. We believe that GH administration may present a new and more physiologic approach to the treatment of erectile dysfunction after radical pelvic surgery.
http://www.midwiferytoday.com/forums/topic.asp?TOPIC_ID=5542
AAS are amazing regenerators - GH may be good as well but you usually hear guys say they get better gains with AAS.