I still can't understand how anyone would leave any antlers that they were planning on keeping at a processors. Why would you do that? There is no reason for it.
I'm not sure about other states , but here there is a damn good "reason for it" , it's required by law. When we tag a buck , the tag is attached to the antler , the registration tag is also attatched to the antler. Both tags are required by law to remain with the animal.
I've never heard of a processor losing someones antlers, around here anyway , especially considering it would be illegal to transport the meat home without the tags. It would also be illegal to process the meat without the tags.
If I were in your situation I would press legal action imediately. I would bet your antlers would show up real quick. If he doesn't have them , he sure as hell knows who does.