David brings up a good point and one that pertains to how training is conducted vis-a-vis what one faces and what a legal expectation is.
For an armed citizen, even though there may not be a "duty to retreat" in your particular state, if you have distance and time to use a ranged weapon on a guy you are going to have to articulate why you did not disengage.
This could be a problem with adaptation in some of the weapons based koryu systems at the maai generally practiced....the goal in any armed or unarmed defense situation is to a) prevent harm to self or others and b) escape the situation where further harm can occur. When you have the ability to disengage based on circumstances, yet stay and continue the fight you are now engaging in mutual combat. If you stay and get revenge the tables have turned and you are committing assault.
Not always: say in Ellis example he is at a home visit, and dude with knife says he is going to kill Ellis and then dude's own wheelchair bound mother who is there in the room and whom he has been terrorizing and living off of for many years: then remaining to protect her, and doing the kind of damage David mentions, becomes more reasonable....
Being in your own home may make it different, or having to protect your family's retreat in public are other examples.
Still, the advantage of the close combat systems is that they generally contain a number of things that are defending against a sudden violent assault, armed or unarmed, and they often contain a pin or other momentary control while the practitioner draws his own weapon or disarms the attacker. That moment of control can also provide the opportunity to disengage, which is often the most tactical thing to do as well as the ethical/legal thing to do.
It is going to be entirely situationally based.
One thing I do want to clarify though is that you are not required to hit, then assess, then hit, then assess again, and so on. Same with a firearm: you don't just have to shoot him once and then look and see what happens before you do so again.
So an articulation of David's example would very likely be "he just kept coming." I don't mean lie, or being tongue in cheek, but if you are dealing with a crazed attacker (for whatever reason) the broken hand, the shattered cheekbone, the ruptured eyeball may not stop the assault. If you can't get away, and he isn't stopping, you can keep going until he does, and don't get too wrapped around the fact that you are hurting him "too much" if he is still a threat to you and others....provided your assessment of that threat is a reasonable one.
I teach cops and civilians that the best way to get someone to stop being a threat is to use the maximum amount of force that is reasonable first, rather than fiddling around with all sorts of different things until you get there. The second strategy prolongs an encounter and actually increases yours and the bad guys chances of injury.
Getting into firearms here would be a bit too complex (i.e. how many times can you shoot him?) but I hope that this makes sense.