The gun owner here wasn't able to stop the BGs. They shot it out with him and got away. I suppose you're a better shot though- right? But of course you are. BTW: why are you asking me how it would work out if I told the bad guy robbery was illegal or handed him my weapon? Where did I suggest that would be a good idea? Please quote that post.
The goal is to stop the criminal act. That can occur in two ways: physically incapacitating the criminal beyond the capability to continue the criminal act, or taking action to cause the criminal to flee. If during the attempt to incapicitate the criminal, the criminal flees because of your attempts, you have accomplished your goal.
To wait and see how things turn out is not defending yourself. It is trusting in fate to smile down upon you and allow you to escape unharmed. I don't carry a gun because I trust fate, I carry a gun to defend myself. If I was going to trust in fate, I would simply carry $400 in my pocket to give to a criminal to get him to leave, rather than carry a $400 gun and ammo.
In the situation at Denny's, I and my family would be under attack the minute the criminals walked through the door with masks on their heads and guns in their hands. They clearly were not there to order a stack of pancakes to go.
And here's another interesting statistic: you have a better chance of surviving a shootout between criminals and citizens then you do surviving a shootout between criminals and the police:
Fact: 11% of police shootings kill an innocent person - about 2% of shootings by citizens
kill an innocent person.
Fact: "In actual shootings, citizens do far better than law enforcement on hit potential.
They hit their targets and they don't hit other people. I wish I could say the same for cops.
We train more, they do better." - Sheriff Greg White, Cole County, Missouri, Guns to be allowed on campus?, KRCG News, July 31, 2009