Alcamtar
Explorer
I let the players set the tone of the game: if they CDG everyone they come to, then they can expect the same treatment.
If the noble heroes never leave survivors you can hardly expect the evil nasties to be nice! By strict PHB definition a Good person values life and fights to defeat the foe, not kill them; slaying the fallen is evil.
I also take tactical lessons from the players. Frankly they have a lot more time and incentive to develop optimal tactics than I do, and surely NPC foes worthy of their steel are just as smart. If they abuse a spell or tactic, they are assured of an exciting return game!
Anyway if the PCs think CDG is a wise tactic then so be it.
If the heroes have an honorable reputation, leaving fallen foes alive and honoring their commitments, then an intelligent foe is likely to use a fallen PC as a hostage, threatening CDG unless a bargain is struck. If PCs have a dishonorable reputation, CDG at will.
Intelligent foes: CDG since they'll expect a cleric to be nearby or at least a healing potion, and it's always smarter to eliminate a foe sooner rather than later.
Stupid or easily intimidated foes: No CDG unless evilly vicious. If you can't escape, attack the most obvious threat, not the bodies on the floor.
Mindless Undead: Leave no survivors, CDG even if it provokes an AOO, after all you have no sense of self-preservation. Makes zombies a little scarier.
Lawful foes: may race to help their comrades rather than waste time on a fallen foe.
Hunters: Devour immediately, unless distracted. When wolves bring down a sheep they don't keep attacking until the herd is massacred, they all stop to eat and ignore the others unless distracted. A really big critter might be hard to distract too...
Mike
If the noble heroes never leave survivors you can hardly expect the evil nasties to be nice! By strict PHB definition a Good person values life and fights to defeat the foe, not kill them; slaying the fallen is evil.
I also take tactical lessons from the players. Frankly they have a lot more time and incentive to develop optimal tactics than I do, and surely NPC foes worthy of their steel are just as smart. If they abuse a spell or tactic, they are assured of an exciting return game!

If the heroes have an honorable reputation, leaving fallen foes alive and honoring their commitments, then an intelligent foe is likely to use a fallen PC as a hostage, threatening CDG unless a bargain is struck. If PCs have a dishonorable reputation, CDG at will.
Intelligent foes: CDG since they'll expect a cleric to be nearby or at least a healing potion, and it's always smarter to eliminate a foe sooner rather than later.
Stupid or easily intimidated foes: No CDG unless evilly vicious. If you can't escape, attack the most obvious threat, not the bodies on the floor.
Mindless Undead: Leave no survivors, CDG even if it provokes an AOO, after all you have no sense of self-preservation. Makes zombies a little scarier.
Lawful foes: may race to help their comrades rather than waste time on a fallen foe.
Hunters: Devour immediately, unless distracted. When wolves bring down a sheep they don't keep attacking until the herd is massacred, they all stop to eat and ignore the others unless distracted. A really big critter might be hard to distract too...
Mike