The deer dropped and I thought - cool! Then, while reloading that barrel, he got up and bolted. At that time, I got to see the hole in his right side, just down from where the spine would be. By the time I got the gun closed and auto-matic safety off(it was worn smooth and I was wearing gloves - bad move for me, he was gone. I sat down and waited a good 15 minutes., before heading down to the impact site to start tracking him. In those days, I was a good tracker.
I am positive I passed that one dead, while trying to find racks that evening. He was throwing one foot weirdly, is the only way I was able to track him. The next day, all I could do was to continue area searching for him. Did the same the next day, no luck. There was a grizzly or two (sow and cub) in that immediate area so I'm sure it wasn't a complete waste.
Lots of elk and moose have been shot years after surviving a non-fatal arrow wound.
As arrows kill by cutting vital organs, bleeding the animal, if a blood filled organ is not struck and the arrow falls out before infection sets in, the animal will likely survive with a healed wound.
Deer have been seen grazing within seconds of having a super sharp - double bladed arrow pass completely through both lungs. They then drop, or take a couple wobbly steps and drop when bled out. This is less likely to happen with a mechanical or multi-blade broadhead with a chisel point as the point itself hurts at impact before the blades are deployed. That's my opinion on this phenomenon of deer going back to feeding after having a complete pass-through with an arrow.