We specified how Abilities and Effects that cause you to be defeated work by adding the pink bit below:
When a figure Gains Damage tokens equal to their maximum HP, they are Defeated and removed from the board. Figures can never have more Damage tokens than their maximum HP. Adventurers and allied Combatants do not remove Damage tokens once Defeated. If an Ability or Effect would cause an Adventurer to become Defeated, they take Irreducible Damage equal to their remaining HP.