He drops his gun as he falls. You carefully collect your wallet and see that his gun was damaged enough to be inoperable. He is still alive and alert, in some pain, but not bleeding profusely that you can see. Now the question.
This is just an all-around bad situation.
You can't finish him off, as he's no longer a threat to you.
If he is not mortally wounded, chances are he is mobile; if you leave to get help, he'll probably be gone by the time help arrives and may have found his own savior and preached his own story about being assaulted. Now it's your word against his, and he's the one sporting a bullet hole.
If he is mortally wounded, chances are he'll die before you get back with help. Worse, with no one else to secure the scene, some other hiker/hunter/backpacker may discover him and upset the scene, leaving no evidence that it was a defensive shooting on your part. Now you're up for murder.
If you leave him to die, chances are he'll be discovered eventually (dead or alive). If it is figured out that you shot him and having made no effort to report the incident, you'll be charged with a crime.
If you try to take him with you, you may be putting yourself at risk; If his wound is not that severe, he could be coherent enough to realize that he will be charged with armed robbery, aggrivated assault, etc. and decide that he can't allow that. He could simply try to escape, or he could try to kill you first so that you can't report the incident at all. Then he can get himself help and make up any story he likes.
If you do take him to a hospital, police station, ranger station, etc. and they are able to save him, he will likely sue you and win. He can claim whatever he wants to suggest that he had done nothing wrong, and with no witness's, it's back to his word against yours and he's the one injured.
It really would be a lose-lose situation. I hope to God I am never faced with making such a decision.
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