That's a dang shame but glad you found him and know now what happened to him.
If it were me though, I'd have contacted the WO officer in your area and had him give you a permit for the rack so I could keep hunting for another buck. I understand though if he was a main target buck and your buddy just doesn't have anything else to hunt either.
Ron and I talked about this very subject recently and feel when these bucks get into knock down drag out fights that their bodies absorb a lot of stress and that might have been a factor in this bucks demise.