Please stop making this up. The Constitution allows Congress to regulate the process of admission of new states, the creation of a new state from parts of an existing one. It is absolutely silent about one leaving, seeking approval to leave, or in any way preventing one from leaving.
Oh, please. You all are the last ones to accuse others of making things up. The Consitution gives the Congress the power to approve any change in the status of the states, from combining, to splitting in two or more parts, to changing the borders a fraction of an inch. By implication that would include leaving. Why should the ultimate change of status be any different?