“The constitution must be adopted in toto and for ever. It has so been adopted by the other states.” James Madison letter to Alexander Hamilton. Hamilton then read this letter to the New York ratification convention.
Take that statement with the following grain of salt: The Articles of Confederation contained a perpetuity clause and then the very people who wrote it almost immediately replaced it with a constitution for which they couldn't be bothered to include another such clause. This is consistent with their positioning between the Hobbesian/Lockean poles.
Contrary to common belief, Hobbes and Locke mostly agreed that power was accumulated by means of consent and delegation. Where the disagreed was on the perpetual nature of the arrangement. Hobbes believed that The People, having given consent ONCE, were forever bound by that act of delegation because he believed in the continuity of identity of "The People" from one generation to the next, whereas Locke believed that no one generation had the authority to forever bind future generations without their consent. The Founders VERY definitely sided with Locke against Hobbes on this issue. Their use of a "Perpetual Union" clause in the Articles was, as demonstrated by both their words and deeds, an "until further notice" sort of instruction, one meant to deny the central government the power to end or alter ITSELF. It put the government under the operation of an autopilot rather than a deadman's switch.
Nothing in the constitution forbade unilateral secession. The 10th Amendment reserved to the states any powers not delegated to the federal government. Since secession is not mentioned, that is a power reserved to the states. In addition to that, Madison never said at the time of ratification that the express provisos of 3 states reserving the right to unilateral secession were in any way inconsistent with the constitution.
If Madison disagreed at the time, Virginia's statement would not have said what it said.