Originally Posted by
Edax
The reason I made the Edax test "Can the Antagonist progress the story if they destroy the Protagonist? If not, then the Antagonist is poorly written." is because often the antagonist isn't fleshed out enough to exist without the protagonist. In the sequel to Man of Steel, you have Lex Luther, whose every action revolves around Superman in some way. If Superman were to drop dead, the story could not continue because Lex Luther has no established motivation outside of Superman. Maybe he creates Doomsday anyway, but we wouldn't know why. Or maybe he decided to harass Batman, but we wouldn't know why.
Also there are movies like Pitch Black where the Protagonist does indeed die and the Antagonist does indeed take over. It is because both character undergo and arc so that end point is the protagonist sacrificing herself for redemption of her actions and the antagonist taking her place and saving everyone. The point of a well written antagonist is that they should have motives outside of the protagonist, otherwise the story breaks if the protagonist dies. If the protagonist cannot die for the sake of the story, than in a meta sense there are no stakes. Nidhogg would still function as a villain because his character has motivations to continue the Dragonsong War, entirely independent of whether the protagonist lives or dies. You could not say the same about Zenos, the moment the protagonist dies, you wouldn't have the first clue what Zenos would do because he has no motivation outside of the Warrior of Light.