In Michigan, lethal force is authorized when a person is:
somewhere he has a legal right to be, and is not committing a crime, and has a reasonable and honest belief that he or some other third person is facing an imminent threat of severe bodily harm, sexual assault, or death.
Furthermore, the lawful usage of lethal force does not grant the user a "License To Kill." A user of lawful lethal force is only authorized to "shoot to stop the threat." Accordingly, once the threat to the user's safety has ended, so too must end the defense. After all, once a threat has ended no further defense by the victim is necessary.
It is understood that an assailant may die as the result of a lawful defensive action, however, that was not the demonstrated intent of the victim. The intent was to stop the threat. Accordingly, each incident has to assessed for legality based on the specifics of that case and other variables: number of assailants, presence of weapons, size disparity, gender disparity, age disparity, and etc.
The law does not specify how many times an assailant can be shot, as long as the threat exists. It could be necessary for a victim to shoot a would-be assailant several times to stop the threat. In many cases, predators wear heavy clothing or are under the influence of drugs that inhibits their ability to feel pain. In other cases, one direct hit may be all that is required to successfully mount a defense.
A self-defense claim can be compromised if the victim "goes too far" by continuing to shoot someone who is no longer a threat to her safety. In one case study, taught by an attorney in the Concealed Pistol License (CPL) Class that I conduct, a victim finds herself in a life-or-death situation in which she is forced to defend herself with her firearm.
In this specific case, her handgun had an ammunition capacity of 12 rounds but her "assailant" had 16 bullet wounds. The obvious conclusion is that she had to reload her firearm, at some point, to shoot her attacker that many times. The problem arises when the shooting is investigated by the local police and the County Prosecutor. It is hard to convince investigators that someone with 12 bullet wounds was still a threat to her safety.
It is plausible to argue that a life-or-death scenario does not afford a person a great deal of discretion when using their firearm against a threat. If she had just shot her assailant with the rounds already loaded in her firearm - up to 12 cartridges - she probably wouldn't have been charged with manslaughter. The Prosecutors had a hard "buying her argument" that her assailant was still a threat after being shot 12 times and that she needed to reload her firearm to shoot four more times.
Michigan law authorizes lethal force under a narrow band of circumstances until the threat has been ended. By definition, a person can no longer be defending himself against a person who is no longer a threat. The scenario, if carried too far, could cause a role-reversal where the victim can become the aggressor and ultimately face a murder charge. If you have an interest in learning more about the lawful usage of lethal force in the state of Michigan, you should take a bona fide CPL Class from a credible and knowledgeable firearms trainer.