Sometimes, it did depend on the situation.
If the pcs were only trying to escape with themselves intact, most often, they would leave incapacitated, but not dead, enemies behind as they continued fleeing.
Excepting that situation, most often, my pcs would make sure they were dead. Sometimes they did not and allowed the enemy to escape. However, if it were monsters, they'd make sure it was dead/destroyed.
If they were hunting for bounties, then it depended upon the reward. Sometimes I'd have rewards posted as "Dead or Alive" then a smaller line of text would be "But twice the reward if Alive." Then comes the fun of them making sure their quarry did not escape before collecting on the "Alive" reward instead of the "Dead" reward.
rmfr