If he turns and runs, never mind that he threatened your life and comitted a felony, let him go to rob, rape and maim your friends and neibors - thus says "The Law." Makes perfect sense, dosen't it?
No, it makes no sense at all, I agree totally. And it stinks. But if the 'immediate' danger to yourself (or loved ones, friends, neighbors, ect.) is removed, then you have no legal right to use lethal force. Especially on the assumption that he MIGHT hurt someone else. Now if you SEE him trying to hurt someone else, that would be a different story.
I know the urge to teach the scumbag a lesson, and send a message to other scumbags is hard to resist, but they just don't let us impale criminals outside the town gates, or stick their heads on pikes anymore as deterants to other criminals.