If the US Constitution had contained a no state secession clause IT WOULD HAVE NEVER BEEN RATIFIED.
You, and I, have no way of knowing that. In fact, considering that the Articles of Confederation did say the Union was perpetual, and the states ratified that, I think most likely they would have ratified the constitution with such language.
Also James Madison’s letter was read to the New York ratifying committee by Alexander Hamilton. So they certainly knew the father of the constitution meant for it to be forever.
And yet it doesn't (contain a secession clause) and it was ratified.