I don't think he'll live. I once was way off on my mark trying an off-hand shot at a doe a loooooong ways off. I should have taken a kneeling rest... something other than standing. I hit her low in front of the leg in the lower chest. I used a .243. She ran about 40 yards and bedded down. I gave her a little time and when I walked up, she put her head down trying to hide. I dispatched her and was amazed she was still alive, but after seeing the shot, I can see why she didn't expire immediately.
I think your buck will be out there dead when you take up the trail in the morning.
Good luck friend. I know it's frustrating, but the tracking is not over yet!
iSnipe