If you have an account which is inactive due to a lapsed or cancelled subscription, you can reactivate the account without losing any test data by simply placing an order for a new subscription. Make sure you're logged in to your existing account when you purchase a new subscription, that way, you'll be able to begin completing tests again straight away.

Provided you have not deleted the account, all test data will remain in the account whether or not it is linked to an active subscription.