[Double Naught Spy]

You brandish firearm and guy's eyes go huge and takes off. No justification for discharge of firearm, guy runs like devil on his tail.

Of course you had reason to discharge your firearm. You were threatened by a person with a knife and in close proximity to you that could do serious bodily harm or cause your death, or that of your girlfriend.

As for the guy later sneaking up on you? Sure it could happen. It won't happen often, but there isn't anything preventing the guy from attacking you again, especially since your situational awareness went to hell and that you assumed that the guy was completely alone. You should have assumed that he would have allies and remain on guard until you are safely away.

Many criminals are cowards and only like easy pickings. You with a gun and him with a knife is not in his favor. Secondly, he won't grope you for your firearm. He will probably jam his knife in your back and then take your gun.

Actually, most criminals are no more cowards than many professionals who deal in violence. Are snipers cowards because they shoot from concealed locations, often at quite long distances, such that enemy has little or no chance to fight back? No. Are members of the airforce cowards for dropping bombs from 50,000 feet, so high that the Iraqis could not see or hear them and didn't know they were there until the bombing started exploding? Nope.

Sure, criminals like easy pickings, but that does not make them cowards. Suggesting the bad guy is a coward is really something of a value-laden under estimation. We call them cowards because they are doing something we despise, but if they were truly cowards, they would not be engaging in close quarters conflicts.

The notion of easy pickings actually has a strong biological risk-reward component. While there are some highly skilled animal hunters like lions and cheetahs, if given the opportunity, they will scavenge a carcass if one is available instead of trying to hunt. When they do hunt, they tend to opt for young animals, old animals, or sickly animals. They are typically slower animals and less likely to harm the hunter. For example, when hunting zebras, the hoof blow from a healthy adult can actually kill the predator, that is why they go for easy pickings. The risk is much less.

I think the general concensus is that in this stuation, no, you do not need to worry about a second round.

This is also an under estimation of the bad guy(s).