That’s why it was called a “perpetual union” and later a “more perfect union” - because it was meant to be enduring (AKA permanent).
And yes - the states (individually) DID surrender a portion of their sovereignty when they became members of the union.
They hoped it would be enduring. Hoped. It was an experiment. A more perfect union means “better”. They hoped the constitution would improve things.
The states DELEGATED a portion of their sovereignty only...the enumerated powers and no more. They reserved all others and specifically reserved a right to secede.