Thanks for all the input guys. We just got back a few minutes ago. We looked hard for about 5 hours and did not find him. We jumped a big buck that looked pretty healthy as he ran away, so we are not sure if that was him or not. If it was, he should have a good chance of surviving.
I was able to slow the footage down frame by frame on my 27" imac and he was definitely hit in the leg. Not sure exactly where, but it looks like it was just about as high as you can get without getting into the vitals. My son has killed a pile of deer and this one is the first deer he has lost. It is also his biggest. I think he was just a little rattled and probably jerked the trigger. Whatever the reason, he made a poor shot. When he gets home from school, I will talk with him about it and let him know that it happens sometimes and hopefully it will be a teachable moment for him.
It sucks. I have a lot of trail camera pics and videos of this buck and it was one I have been after since the season started. I finally figured out what he was doing and the plan worked perfectly yesterday, all except for the end result. Hopefully he will survive and we will catch up with him later down the road.
Thanks again for chiming in.