Hey!
The release notes for Commander 2018 state:
In a multiplayer game, if a player leaves the game, all cards that player owns leave as well. If the player under whose control Xantcha entered the battlefield leaves the game, the effect changing control of Xantcha ends.
The last sentence doesn't mention what happens after that effect changing ends. My understanding is that based on rule 800.4a, it is exiled, as there is no previous controllers who would regain control of Xantcha:
800.4a When a player leaves the game, all objects (see rule 109) owned by that player leave the game and any effects which give that player control of any objects or players end. Then, if that player controlled any objects on the stack not represented by cards, those objects cease to exist. Then, if there are any objects still controlled by that player, those objects are exiled. This is not a state-based action. It happens as soon as the player leaves the game. If the player who left the game had priority at the time he or she left, priority passes to the next player in turn order who’s still in the game.
However, the ambiguity of the release notes made me second guess myself, and wondered if the default mentioned in rule 110.2 should apply, and that the permanent's owner would now be the permanent's controller:
110.2 A permanent’s owner is the same as the owner of the card that represents it (unless it’s a token; see rule 110.5a). A permanent’s controller is, by default, the player under whose control it entered the battlefield. Every permanent has a controller.
Clarification would be welcome, thank you for your tireless hard work.
- Emilien