Rule 383.2.c.3
If a Game Object has a Triggered Ability whose condition is the Game Object leaving the board, such a Triggered Ability is processed immediately before the Game Object changes zones. Example: If a game object has a deathknell ability, which triggers on the game object dying, it will be processed and placed on the chain just prior to the game object being placed in the trash, during the event of the game object dying. Example: Treasure Trove has a triggered ability that triggers as it “leaves the board.” Such a triggered ability is processed and placed on the chain just before Treasure Trove completes the action of leaving the board by being moved to another zone.