Does Netsuite have an archive option where you can keep an instance(account) just for archive not operational/active account?

I've heard yes from a customer considering leaving the platform but the cost was so high they might as well stay

that figures netsuite

I have not seen it. In fact, one customer licensed a 2nd instance that turned out to not be required and had to honor the contract even after growing the user count by 150 on the original instance.