You can cancel or upgrade at any time. If the subscription is canceled, your account will have no subscription after the subscription period ends. The extension settings will stay saved and won't be deleted. Also, any extension that you create while you have no subscription will still be there when the account is upgraded again.
E.g. the transaction was blocked by your bank or the card has expired.
If there is a failure to process the credit card payment for your subscription and you failed to update your card information in time, you will receive an email informing you about it. We will retry to charge your card for two more succeeding days. If the transaction is still unsuccessful, your subscription will be canceled.
If your account is on one of our legacy plans, you won't be able to get that plan anymore. Once your subscription is canceled, you'd only be able to subscribe to the new rate when you come back. You'll need to go to miniExtensions settings to buy a new subscription again with the plans currently available.