"If"? It was widely understood to be fact.
Here you have Virginia's ratification stating they could resume their own governance.
may be resumed by them whensoever the same shall be perverted to their injury or oppression,
Here is a ratifier from Virginia, John Taylor:
The deputations by sovereignties, far from being considered as killing the sovereignties from which they have derived limited powers, are evidences of their existence; and leagues between states demonstrate their vitality. The sovereignties which imposed the limitations upon the federal government, far from supposing that they perished by the exercise of a part of their faculties, were vindicated, by reserving powers in which their deputy, the federal government, could not participate; and the usual right of sovereigns to alter or revoke its commissions.
Another Virginian, James Madison, said that secession was nonsense.