Can 'o' worms......
Very true that you can't just shoot someone who walks away...unless...
What if he's got a weapon and just comitted a violent felony. He's got the gun/knife/bloody bat in a down or low ready type position. You draw and shout a command "Drop the weapon!" You're about to shoot, transitioning your weapon to good sight alignment, moving your finger from the frame to the trigger..... He looks at you and turns to walk away, still holding the weapon....now what?
However, same scenerio....you draw...shout "Drop your Weapon!" The perp looks at you, and drops his weapon. Now what? Holster your weapon and go call the cops?
No. You've got to be prepared to give the perp commands and hold them at gunpoint until the "Authorities" arrive.
The only way to stop him from killing me was to run over him.
Never, ever, ever take on a vehicle unless they are already trying to kill you! Unless you score the magic bb, you're
not going to stop a vehicle with a typical CCW handgun!
The damage is done and the guy is fleeing (the 'run' part).
My opinion, and thats all it is, is that
if the guy still presents a serious danger to other persons or yourself. Like if its a crowded parking lot, and he's bouncing off cars trying to get himself out of there...or hitting more people, or barreling down on you as you attempt to render aid to the first victim(s). And you still need to consider all the other tenants of applying deadly force. Can you evade/break contact? Do you know what's behind the target....etc etc...