I've seen several instances where a neck shot with a gun drops them only for them to get up later unexpectedly and never found again. My uncle actually hit an 11pt in the neck with his bow one year, dropped him in his tracks. He put another arrow in it just to be sure, and hit the shoulder blade. He thought it was down for good until an hour later it jumped up, shook off and wasn't seen again. Luckily a couple weeks later he got a chance to finish him during gun season, the buck was alive but really hurting and wouldn't have made it through the season.