Well, to start with the last first, the chances of this happening (shooting an antler off) are so remote that I don't think it really bears discussing.

As for the injured deer, I have taken that had one front leg broken and one back leg shot. It was all it could do to hobble a few feet and then drop. (It was bedded down when I happened past it.) It was not legal as it was a little spike. I was about 16 at the time, but I knew the right decision. Later, my father and I explained what happened to the local game officer and I gave him my buck tag. That was the end of it. I knew very well I could have been fined.