Game concept
Character Death
The game also links it as Dying, Die, Dies, Death, Deaths.
From the game's encyclopedia
Death triggers Succession, which is important for Rulers.
If a Player Character dies, the player will continue playing as their Player Heir — or be faced with a Game Over, if they have no valid heir.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Character Death is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Death triggers Succession, which is important for Rulers." It covers Natural Causes, Religion, Combat and Murder. The game also links it as Dying, Die, Dies, Death and 1 more. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.