The first time I hunted with a muzzleloader, about 10 years ago, I spine shot the biggest buck I've seen on my property while hunting from the ground. When I approached him, he kept turning away so I couldn't put the finishing shot in the lungs, so I shot him in the neck. I sat near him for a few minutes waiting for him to expire, and to my great surprise his back legs started to work, and he lunged forward, almost getting me with his antlers. I didn't have another round (learned THAT lesson), and by the time I got back to him with more ammo he had moved about 50 yards. He got up and ran like he was unhurt, flagging and snorting, and I haven't seen him since. I followed his running tracks, no blood I could see, for about a quarter mile before I lost the trail.
My ex wife once shot a young buck near the spine with a rifle. He went down, kicked a bit, then got up and ran off. The second shot hit his chest and did him in. Oddly enough she had nicked the same buck in the neck two weeks before from the same stand.
A "spine" shot is not necessarily lethal, if it misses the spinal cord. Sometimes it just stuns them, so a follow-up shot should ALWAYS be taken.