The worst part of that story is that most likely he will be fired from DG as a result. They are pretty strict with their no gun policy. I worked at one that had been robbed at gunpoint twice before and they were adamant that you just give them the cash and "hope" they walk out without shooting anyone.
I had it in mind to keep a can of wasp spray (aim for the head, 10 foot + shooting range) by the counter in case, but never actually did. Scene played out well in my head, but who knows if it would have been successful in real life.