The US Constitutions is silent on the subject of secession. This makes it up to the states to decide. If they vote to leave then they can go. I have no problem with any state wanting to go on it’s own. Vaya con Dios. Stopping a state from leaving is not worth spilling even one drop of blood over.
No that does not automatically leave it up to the states to decide. The 10th amendment delegates power to either the states OR the people. It doesn’t spell out which has what power.
People who argue that secession is legal always leave out the people and pretend states retain all powers.