I can't say why Sudden Impact died, but I can guess until someone else posts something otherwise.
When I was there earlier this summer he had a hard time holding his head up. So when he was laying down he would let his head rest on the ground. It looked just like he was dead laying there. I can only assume that since velvet and antler in summer is just growing tissue that any scuffs and scrapes would cause a possible infection or at the very least an open wound if bad enough. I had heard (again I don't know for sure) that he had maggots and infection in the antler and they knocked him down the treat and remove. But then he died later anyway.
I had also heard that Wesson had a major infection in his eye. I think they said he had been poked in the eye by a branch, but I might have that wrong. I think they even had to remove the eye. Sometimes bad things just happen. Wesson was a great buck that was making nice progression each year. I like bucks that make those nice even jumps each year instead of the ones that are big yearlings and then just never get bigger.
It is a sad case for each buck. All any of us can do is try and keep them all healthy.