You posts only prove one thing. You have no concept of the original intent of the USC to create a republic. The concept is totally lost on you. Unfortunately you are not alone.
Oh, I agree that the Constitution created a republic, or if you prefer a “res publica” a public creation. Such a republic could no more exist with ‘at pleasure’ secession than a corporation could exist with ‘at pleasure’ dissolution by any of the stock holders.
Since the a supermajority of the states was required to create the republic, simple symmetry would require a similar supermajority of the states to dissolve it. That could be done by constitutional amendment.
Because the constitution has provisions that describe limitations on Treason, then treason must be possible. No defense against treason along the lines of ‘I decided to dissolve the republic, and thus treason does not apply’ is applicable.