Mike, I would bet the law requires the "defender" to stop when the threat is neutralized. Being attacked is not a license to 'punish' your attacker, only to defend yourself. Otherwise, someone could claim he was attacked so he could beat the snot out of someone he did not like. At some point, "defense" becomes "assault".
In rereading your post, it would seem that the instigator gives up his right to life by instigating the assault. True? Not all assaults justify the use of deadly force.
But then, I do not know your state laws. And I can recall when it was still illegal to drive a car in Massachusetts without a flag man on foot 50' in front, to keep the horses from being scared. So there are a lot of strange laws still on the books.