Ahahahaha!
Hilarious!
I think someone failed his reality-check. Sure, it's annoying when an enemy runs away (my players hate me cause their final boss - a Topaz Great Wyrm - got away with like 16 hp. Though he left his hoard behind), but it's only natural. The enemies aren't supposed to be killbots that are programmed to fight to the death. Most aren't even berserkers or some knights or something who "never flee, never surrender". Most people will see that "That bastard with the big sword just very nealy took my arm! I'm no match for those guys. I think I rather run away than die."
Of course, the DM should be sensible about it: Limit it to reasonable escapes. They run away, yes, and a spellcaster may have word of recall or teleport, but not every 1st-level warrior has that kind of resources, they have to flee per pedes. And someone who's hit in the head with a scythe (i.e. brought to under 0 HP) won't flee nowhere. So as long as it's believable that the guy can pull it off like that, and that they don't survive at -85 after my crit to run away, no matter what you do (I actually had that once), I'm OK with it.
Also, there will be some who want to fight to the death: Berserkers in frenzy (and similar stuff), enemies adhering to a certain code, people who know they have nowhere to run, or others who defend something - or someone! - they hold dear.