When you need to be absolutely certain that an enemy isn’t going to get back up again, you can deliver a coup de grace to ensure they are properly dead.

To execute a target, place your weapon on a creature that is Bleeding Out or otherwise lying helpless on the ground (the Stunned condition does not count, but being tied up or otherwise restrained does). Then say in a loud, clear voice “Deathstrike 1, Deathstrike 2, Deathstrike 3, Deathstrike 4, Deathstrike 5, Excecute.” Try to pace the Deathstrike calls to 1 second each. If you are attacked at any point before you finish saying Execute, you must start over again. If you finish the Execute call, the target immediately dies.

Note that enemy NPCs may return to the battlefield after being executed, but this should only occur when they are respawning, at which point you can consider them a different character from the one you executed.