Comprehensive Rules
508.4b
If the effect that states a creature is attacking specifies itâs attacking a certain player, and that player is no longer in the game when the effect resolves, the creature doesnât become an attacking creature. The same is true if the effect specifies a creature is attacking a planeswalker or battle and that permanent is no longer on the battlefield or is no longer a planeswalker or battle when the effect resolves.