Rule 901.10 · Planechase
When a player leaves the game, all objects owned by that player except abilities from phenomena leave the game. (See rule 800.4a.) If that includes a face-up plane card or phenomenon card, the planar controller turns the top card of their planar deck face up. This is not a state-based action. It happens as soon as the player leaves the game.
Subrules
If a plane leaves the game while a “planeswalking ability” is on the stack, that ability ceases to exist.
Abilities from phenomena owned by a player who left the game remain on the stack controlled by the new planar controller.