Does an oath against leaving conditional upon the permission of a specific person break if that person dies before permission is granted?

Primary text

If a person swears that his wife shall not leave unless Zayd gives permission, and Zayd dies without granting permission, and she then leaves, the oath-taker is held to have broken his oath. This is because the oath was conditioned upon an event that did not occur, and the contingent action is not permissible without the condition being met.