“If a state leaves the union it is no longer the territory of the United States.”
That is pure nonsense. You cannot just unilaterally, arbitrarily, and prejudicially abrogate the Engagement the State with its ratification entered into the joinder of territories with the other States in the perpetual Union. Proposing such a state of affairs involving unilateral secession of the State is nothing less than lawlessness, alienation of the State, and treasonous rebellion prejudicing the rights and duties of the member States of the perpetual Union. To regain or recover the sovereign powers the State previously delegated to the perpetual Union of the United States, the State must obtain the consent of the Congress assembled and the member States of the perpetual Union. Only when the State has lawfully recovered the sovereign power it delegated to the perpetual Union can the State lawfully withdraw from the Engagement it previously made and proceed on to secede as a sovereign state with all of its sovereign powers recovered from the former joinder with the other States of the perpetual Union. Until that occurs, the territory of the State is cojoined with the Territory of the perpetual Union of the United States as with any delegation of sovereign powers to the joint sovereign nation.
Perpetual union? I didn’t see that in the Constitution either. You must have a different copy than I am looking at.