I think it will be a good leason for him. Next time believe him a little more and treat it like you saw him hit it and don't give up so easy. I lost one two years ago that a buddy of mine shot as his first deer. We found blood but I couldn't find her. Blood ran out after 100 yards and it was so thick I was crawling. Never found anything. At least he knows he killed his and fed some coyotes! Its a good nature leason of how nothing goes to waste in the wild.
Stuff happens. No need to live in the past. Focus on getting him his second one and finding it so you can see the look on his face when you tell him to gut it! (my dad still laughs about it)