RE: Fatal hit or not???
There's no doubt that with the caliber you are shooting and the bullet you are shooting that at that distance the bullet exited. There's know way, regardless as to where you hit the animal, that the bullet you are shooting would fail to exit.
That being said, it makes more sense that you would have hit the deer low instead of high because of bullet trajectory vs. line of sight. Maybe just clipped him through the brisket or something.
What did the animal do when you shot? Did he hunch up? Did he jump? Did he look like he staggered or fall down? Did he kick? Did he run like a scalded ape like he wasn't hurt? Did he have his tail up? How long were you able to watch him before he went out of sight? Was he "flickering" his tail?