Hi Pietro3000,
You can not finish ITM without being dealt a single hand. In effect, player 12 has not participated. Registering in and of itself does not make a registrant a participant. In order to become an official participant of a tournament you must have played a hand. Not merely to have registered, or even to have had your stack dealt in. You must physically be present and have looked at cards and acted upon a hand (Check, bet, fold).
In this situation, you refund player 12 and payout players 11 and 10 according to chip count if the players busted on same table or by combining the prizes of 11th and 10th and chopping equally between 11th and 10th finishers.