As a rule, I don't GAF about escape, and even in LE, most of the time I did not. I would have to absolutely KNOW for sure that the escaping person was one truly vile and dangerous criminal to care. Garner, despite the manner dishonest plaintiff's lawyers and gullible judges in some settings (9th Circuit, which I plan to leave when I retire) have expanded it, simply does not apply to private citizens. While some states changed their laws after that decision and made LE and civilian use of force the same, others did not, and left it so that cops were more restricted. That has nothing to do with defense of self and others.
In the scenario Dave Keith described experiencing, the response Iggy described is sound. If that time comes, put shots into the vital areas as rapidly as you can until you perceive the threat is controlled (which means the offender is incapacitated). Most likely, at close range as is likely here, some number into the center of available mass, and one right into the face, or ear, or other line directly into the brain, as rapidly as you can do with adequate precision, is the answer. (Pistol rounds suck - other than the brain/CNS shots, you need to plan on 3-7 shots into the offender as fast as you can in order to prevail.) If you cannot do that because you are not confident of your skill, the law, the ethics, whatever - that choice is already made for you.
In others, standing there like a lump and doing nothing but observe is sound. We should not care enough about the store's money to do something stupid, as much as I dislike the trend toward letting criminals engage in their actions with little risk.
If you have the ability to carry lawfully, you darned well better have considered such issues at length, become familiar with legal, tactical, and ballistic issues, and made up your mind before carrying, or you need to not carry until that time. There is no in between place. You are either prepared, or you are not.
ETA: If one looks at the number of violent crimes committed in the US (I've linked the data before, but don't have it readily at hand now; google the Bureau of Justice Statistics victimization data, IIRC), it is pretty clear that victims, like cops, don't shoot anywhere near as many offenders as they could (and by necessary implication, should).