My advice is get over it for now. Most cut guys couldn't care less (because they don't know what they're missing).
BUT, there may come a day when the weight of what he has lost will sink in with him and HE will have some grieving to do. THAT is when you need to do your grieving and feeling bad. Until then whistle past the graveyard.
And another thing, about this "he wouldn't know what he is missing" comment. I would highly recommend her to talk to her son when he is older (in his teens, perhaps) and explain him in a gentle way what exactly was taken from him and what are the usual consiqenses. This way, first of all he can make a choice whether he wants to restore (of course I'm talking about the non-sergical restoration...OP ask Ron--yes this very Ron whose post I'm critisizing here --about restoration, he is an expert in the area, so you know what's possible when your son is older). But what's most important is that her son will understand that this is not something that should ever be done to his sons. A friend of mine talked to her 12yo about circ, explained to him that she didn't know any better, appologized to him. The boy thought for few minutes and said that it is sad and that he will not do this to his kids. 5 minutes later he was happily playing ball with his friends. It really is that simple. My son is 5 and a question of vaccines came up not that long ago (he asked me what those shots some kids were talking about were). I explained him in a way that he could understand and I told him that when he was a baby I didn't know any better and did allow him getting some of those shots. I told him that I regret it deeply even though he is fine (beyond his eczema that started with the shots), I appologized to him and let him know that his sister is vaccines-free. I also told him that I would never allow this happen to him again. He totally understood everything, including my deep regret. The next second he was playing like the conversation never took a place. Kids know that we--their parents--aren't perfect, but they love us and they know that we love them to death. And you know what, with all our faults and imperfections we are still perfect to them.