Maybe a "delete this game" option at first turn only (after you see all the involved nicknames) ... or even a "delete my plane from this game ... (less painful in a 10 players game ... even if not for your fellow pilots).
This seems the best solution: unsubscribe during the first round. This would be helpful also for when someone mistakingly enters the wrong game, as often happens. I don't think it would be too hard to implement, too.
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