I'm not disagreeing with you outright, more so pointing out your wise usage of the word "may". You may not be held responsible, and that is true. But we've all seen the courts make some wrong, unjust decisions in the case of self defense. I know a guy who was doing a martial arts demo, some asshat from the audience came at him unprovoked, he responded by hitting the guy once....and the asshat hit his head on a concrete bench on the way to the ground. He stated he was defending himself. The prosecuting attorney for the family brought up his martial arts training, saying how he should have been able to deal with the guy 'differently', and ultimately, the karate guy went to jail for involuntary manslaughter. You never know how a judge or jury will react to your use of a firearm.If you accidently injure or kill someone while using deadly force to protect yourself, you may not be held responsible for this. It's going to depend upon in which state the event takes place. In my state, Virginia, the person who would be criminally liable if this were to happen would be your assailant and not you.
As for civil liability, well you can be sued for just about anything but the chance of being sued for something like this may be pretty remote if your actions to save yourself from serious bodily harm were found to have been justified. Still it never hurts to have insurance for such things.
As for civil liability, the bar is lower than in a criminal case, the key is pointing out your justification for the use of force and that level, as well as mitigating factors (did you perceive his threat accurately according to the circumstances, did you have an opportunity to safely retreat, etc.).
This is a worthwhile discussion that we should all have with others and within our own minds.