...you are presuming that the guy with the plastic gun, empty gun, one who has absolutely no intention of shooting at the cashier is a serious danger.
One has no way of knowing the intentions of an armed person who is committing robbery. One only has reason to believe that he has both the ability and the opportunity to kill or seriously injure, and that he has placed the victim in jeopardy.
In the eyes of the law, a person who has reason to believe that a person who is robbing him is armed presents an imminent threat of death or serious bodily harm.
In the scenario at hand, the possession of a weapon by the robber is a known fact.
It is
possible that the robber has no intention of using the weapon.
Perhaps the likelihood that he would use it is rather small.
The defender
might choose to bank on that possibility. Most people would not consider it prudent to do so, however.
The real risk is that at short range, the defender would not be
able to defend himself or herself in time.
That's why it
might be wise to not force the issue and just hope for the best.
But that's a real gamble.
So is trying to draw and fire at someone in close proximity who is armed with a contact weapon, and if a threat has been made, the odds are not for the meek. We do not know the layout, but if it is at all possible, the defender would be well advised to try to put some distance between him or her and the robber while drawing, and to do so without delay.
The Tueller drill has been mentioned here. Has anyone here tried it? Would you really like to expend some of your very limited time fiddling with cash and trying to divine what will happen next before doing something about the threat?