Arachnoid cyst draining

I had a friend who recently had a arachnoid cyst drained (he is 15) and now has complete memory loss..basically he is a shell of whom he used to be. He is still in the hospital and may get out soon. I guess my question is ....is this common for this procedure? Will he regain any memory..? I am just searching for something so my friend will remember all the good times we had before he went in. I understand the need for the surgery he was experiencing many painful days and nights..nosebleeds, blackouts and went a few months being misdiagnosis and the family knew of the risks, but never seen this coming.We were all blindsided by the outcome. Can anyone provide any aspect on this or know of someone that "came out" form this devastating procedure?