What is obligatory for the one who is prevented from completing his Hajj if he has already performed the obligatory Hajj?

If the one who is prevented from completing his Hajj has already performed the obligatory Hajj, what is required of him?
He owes nothing; he simply completes it. If he is able to complete it, he completes it. If he is not able to, he slaughters his sacrificial animal and either shortens his hair or shaves it, and then exits the state of ihram. When the Prophet (peace and blessings be upon him) and his companions were prevented from completing their Hajj, he did not say to them, "You must perform 'Umrah." He ordered them to slaughter their animals, shave or shorten their hair, and exit the state of ihram. Then, he performed 'Umrah the following year. They called it the 'Umrah of the Covenant, but he did not obligate anyone among the people to perform it. He performed 'Umrah with those who performed it, and it is not established that he obligated anyone to make it up.