I was thinking of a scenario where, instead of trying to draw and return fire immediately, you take cover and shoot. If you are with someone, they may be next to you behind cover and able to assist. I've never been in this situation (and hopefully never will be) but if someone came in to some location and began firing, I think my first reaction would be to protect myself by getting behind or under something and then returning fire when most advantageous to a more favorable outcome. I may be the only hope for the lives of everyone there and I'm not very useful dead. However, I often get the impression that as time goes by, the less likely I am to be the only CHL holder in ANY location.
However, the point of this post was more about the legal ramifications of such actions as opposed to the practical application.