I have lost a few in my long hunting life and they always haunt me. My most recent was a similar situation as the OP. It was ML season and I had a standing broadside shot with a rest at slightly less than 100 yds. Took the shot and the deer dropped kicked a few times and stayed down in 6" deep green field grass seemingly dead. There were 2 of us and we had around 10 minutes of legal time so we just sat hoping for a double kill. I called the landowner and told him I had a deer down and he said he would come down and drag it out with his wheeler. After a quick 10 minutes nothing else came out into the field so we unloaded and climbed down the shooting shack ladder. We hit the ground just as we could see the wheeler lights come over the hill. We started to go towards where the deer was and suddenly it stood up and took off much to our amazement. Our guns were both uncapped and the wheelers headlights showed that deer racing for the swamp. 3 of us looked until around 11 that night and found only a little blood at the spot where it was and couldn't find anything else. I went back the next day and spent all day walking that swamp which was pretty thick and never found a trace of the deer. I kept an eye out for a few days and never saw any crows or ravens which would have found that deer if it died. No clue what happened but that one will stick in my memory banks for a while.