When you train you need to train for taking out a dedicated opponent, and dedicated opponents are nothing like deer. It's been my experience that most stories where the BG runs off he was either surprised to see a gun and ran (as was the case when a few guys tried to mug me a few years back) or he didn't know the good guy was even armed until he took a round and then he beat feet. Generally, if a man stays on scene after you pull a gun, you can assume he's "in it to win it". If you're not comfortable with a 9mm or above, then by all means please carry a .380. Just realize that your response shouldn't be a "controlled pair". It needs to be a mag dump or a face shot. This policy is meant to keep you alive in the face of grave danger, and you can't wait around to see if he is the "run away!" type. So just train until you can't get it wrong.
This^^
If it's bad enough that you actually draw, things are bad. If you actually need to fire, then you better empty your mag. NEVER shoot to injure. You shoot to stop the threat. Stopping a threat means incapacitation. That means no ability to any longer post a threat. That doesn't mean he can't use a hand anymore or that he can't walk very easily. It means he CANNOT harm you because he lacks the physical ability to.
I'd like to think even a determined BG can't stand 15 rounds of 165gr HST. But if they aren't well-placed, even 15 "hits" can be insufficient--even with a nasty load like the HST.
If I'm in a situation like this, I'm aiming not for COM, but for the hips/groin so he can't run at me (and a femoral artery will bleed out very quickly). If he's armed, and the range is reasonable close, I'm taking head shots.
COM hits just can't incapacitate fast enough to stop someone from killing me. Even a direct shot through the heart can let the BG keep coming at me for anther 10-15 seconds. No, COM hits aren't instantly incapacitating. A shot between the eyes usually is.
What's the movie line? "Aim small, miss small"