I'm glad this ended the way that it appears that it did. Something to think about, though,is that there are somewhere around 175,000 armed robberies in the US every year. In the vast majority of those no one gets injured. Most thugs just want to inimidate long enough to steal and then get away. Killing or injuring usually happens with resistance.
If you are robbed when by yourself then absolutely pull your gun and start blazing away if you get your chance and feel lucky-I hope it turns out like this one. But if there are others in the area, like the first clerk that gets caught in the crossfire, it might be wiser to hand over what the guy wants and be a good witness.