If you are truely defending your own life or the life of another, you never, ever shoot to kill. You shoot to instantly stop the threat to your life. That is accomplished for the sake of this topic, by shooting the assailant. Shooting someone is deadly force, because obviously it could most likely result in their death. If the assailant dies as a result of being shot, that is secondary to immediately stopping the threatening behavior. Having said that, you target an area of the assailant that has the best chance of accomplishing the task. That in most cases is center of mass. The chest and upper torso area. Secondary is the head and pelvic area. You do not target these areas because they are most likely to result in the death of the individual, they are targeted because good hits in these areas stops the individual. You do not employ deadly force by shooting the person in the leg, foot, arm, or any area such as that to "just wound him". If you are truely in a deadly force situation, you need him stopped immediately if possible. If you shoot him in the leg or foot, it can be successfully argued that you were not truely in fear of your life and were not justified in shooting him at all. Not to mention, it will get you killed. If the assailant stops the threatening behavior prior to you shooting him, you must not shoot. If you have to shoot him, and he goes down and ceases to be a threat, you must stop shooting. If possible, you need to give him commands as to what you want him to do; such as "Stop!!" or "Drop the weapon!!" You give commands as a warning and to let him know what to do to avoid being shot. You must practice this when you train or you will not do it under stress.
Now lets say you have already shot him. I would immediately call for an ambulance for him and render some kind of assistance to him. Not only is it the humane thing to do, but when you start explaining to the authorities that you were defending your life. It will be obvious from your post shooting actions, that you were merely defending yourself and had no malicious intent toward the individual. It will show that you were not trying to kill him, but trying to get him to immediately stop threatening your life.
I know the macho thing to do, would be to kick him a couple of times, spit on him, and call him an ambulance in a half hour or so. Sure, most people would feel that way. After all he did just try to take your life. But, remember, you not only have to survive the actual encounter with the criminal, you have to survive the resulting aftermath. The investigation by the authorities and any civil litigation that results. You could manage to survive the assault and still lose big if you don't manage the situation correctly.