If presenting the weapon stopped the threat and/or prevented the robbery, mission accomplished!
Armed citizens protect themselves and prevent crimes by simply making the BG aware that they are armed far more often then they do actually firing the weapon.
Thankyou, Billwot. First off, if we only pulled our guns when we knew beyond a shadow of doubt we'd have to shoot, it would be TOO LATE to use it in thousands (or millions) of cases. Second, defensive gun uses amount to millions of cases in this country every year, in nearly all of which no shots are fired. The crime stops with the sight of the armed citizen far more often than not. Criminals are generally cowards who, when faced with armed resistance, turn inside out trying to get away. When they don't, well that's when the SHTF.
So the rule is, only pull when you'd be
justified in shooting. In DH's case, he was compromised by injury and walking with a cane, the BG was big and healthy (disparity in force), the BG had intent, opportunity and ability, thus the draw was perfectly legitimate. You or i might have just shot at that point, and (all the legal hassle aside) it would probably have been ruled a good shoot. But when the dude turned to run away, that justification to shoot vanished.
DH did
REALLY WELL imho, kept his cool, defused a situation that might otherwise have led to violence, robbery or death, and impressed his wife in the process. He avoided a lengthy, costly legal battle even though he was in the right, he kept his money and his pride - i just don't see a better outcome unless you're on a track to eliminate all the scumbags from all the walmarts in the world.