Tiers of “heroes don’t kill people, but we still want the villain to die because something something justice” in ascending order of “well, technically”:
- Hero simply leaves; villain coincidentally killed shortly thereafter by something unrelated. Example: murdered by treacherous minions.
- Villain accidentally kills self while attempting to harm hero. Example: shoots at hero, misses, struck by improbable ricochet.
- Hero and villain’s conflict leads to perilous locale from which only hero escapes. Example: fighting on train tracks, villain hit by train.
- Villain defeated non-lethally; dies anyway due to unpredictable or outside factors. Example: villain disarmed, dies of magic curse.
- Hero employs lethal force, but that isn’t what kills villain. Example: villain evades hero’s attack and falls off cliff.
- Hero deliberately employs environmental hazard to kill villain. Example: hero throws villain into live electrical wires.
- Hero apparently kills villain; later developments reveal villain survived and was killed by something else. Example: hero kicks villain off cliff; post-credits bonus scene shows them getting up and walking away, then getting eaten by a bear.
you forgot the main one where the hero shows he isn’t a blood thirsty dude out for vengeance by trying to save the villain last second, but the villain rejects this and voluntarily submits to whatever was about to kill them
That’s more of a sub-trope – it can land anywhere from tiers 2 to 5 depending on how exactly the villain got to be in that predicament in the first place.