I have been following this thread so I apologize if someone referred to this already and I missed it. When this happened it was discussed on some other boards and someone may remember.....
A similar situation happened in Omaha almost exactly a year ago. A customer shot and killed an armed robber in a Walgreens drug store. Here is a link to a story about the shooting.
Customer Shoots, Kills Would-Be Armed Robber - Omaha News Story - KETV Omaha
I think I remember that he was cited for not having a conceal carry permit.
Here is some more info:
Douglas County Attorney Don Kleine said Tuesday afternoon that McCullough's use of deadly force was “appropriate and justified” and that he would not be charged in the slaying.
“There's no question that he had the right to defend himself and protect the lives of the others in the store,” Kleine said.
Nebraska law allows an individual to use force when his life or another person's life is threatened.
However, McCullough was ticketed by police for carrying a concealed weapon, a misdemeanor.
He had a permit to carry a loaded handgun in plain view for example, in a holster but he did not have a concealed weapons permit, said Omaha Police Officer Jacob Bettin.
McCullough pulled his handgun from the waistband of his pants before he shot Thomas, authorities said.
Kleine said civilians normally shouldn't put their lives at risk to prevent a crime. However, “if someone feels threatened,” he said, “they have the right to defend themselves.”
No one else in the store was injured.
Definitely a real scenario and a decision that you should prepare yourself to make.