Great discussion. I just in fact got my CCW, completed a pistol class, even though I thought I might be ok, its been years since I have been interested in arms and shooting and did not think myself safe to carry.
Just today I was thinking of such a scenario, although in my minds role play I tried to work through what I would do if someone threaten me with a lesser lethal force during a hold up than firearms, ie. maybe a BG pulled a knife. I don't think I would pull my firearm even with that before throwing my wallet to the ground below their feet and running as fast as I could while organizing my thoughts about possibly using lethal force.
First the BG has to choose between chasing me or picking up what they would want, the cash. If I gained some distance and the BG went away, no life taken, cancel the charge cards, say bye bye to any cash and all is well. But if the BG then decided to pursue me further... draw, aim and fire.
Of course its all subjective there are so many variables that would be at play.
-Scott