I would venture a guess that any crook that robs a pharmacy is after one thing and one thing only: drugs, and perhaps any loose money lying around. But it is also a good guess that these are hopped up junkies that have no value to life. If we knew for sure that they would take the drugs/money and just leave, then let them have it. But hop heads are unpredictable and may just indiscriminately shoot someone for the kick of it.
In this particular instance, it is probably store policy for employees not to have guns because of the liability of collateral damage should a bystander/customer become shot or killed by a gunshot from the pharmacist will most likely open up a deep pocket for litigation and civil suits.
If I were the pharmacist, I would have done exactly what he had done. My job is not worth my life. I can always search out another job while my wife and family have a husband, father, and the ability to maintain the family unit. Isn't this the basis for why we all carry?
May the Schwartz Be With You.