Since I am admittedly unable to discern these supposed implications on my own would you please be kind enough to point me to the exact sections and clauses of these articles you believe to contain them?
Article I, Section 10, Clause 1 through 3. Article IV, Section 3, Clause 1. Basically Article IV says that no state may be admitted without the consent of the other states as expressed by a vote in Congress. Once allowed to join, states cannot split, combine, or change their border by a fraction of an inch without the consent of the other states as expressed through a vote in Congress. Article I, Section 10 lists a whole list of actions that could impact the interests and well being of the other states and which are forbidden entirely or allowed only with the consent of the other states as expressed though a vote in Congress. If states can join only with permission and once in can alter their borders only with permission and forbidden from a whole host of actions without permission then it isn't a stretch to conclude that permission is needed to leave as well.