The only way that power could be reserved under the tenth amendment is if the states had that power before the adoption of the constitution. They did not have that power because of their ratification of the Articles of Confederation and Perpetual Union. They agreed to form a perpetual Union(or country if you will) and from that point on could not leave without the consent of the other states.
You are aware that the participants in holding a "constitutional convention" absolutely broke and violated the requirements of the Articles of Confederation which required Unanimous approval by all states? (Rhode Island refused to participate.)
If they would not obey their own laws regarding the Articles of Confederation, then you cannot claim the Articles of Confederation as some sort of governing authority over the powers of the States.