If your billing account remains invalid for a protracted period, some resources might be removed from the projects associated with your account. For example, if you use Google Cloud, your Compute Engine resources might be removed. Removed resources are not recoverable. [1]
During the grace period with outstanding cost and closing the billing account, the system automatically deletes your App Engine instance. This is not recoverable.
[1] https://cloud.google.com/billing/docs/how-to/resolve-issues#resolving_declined_payments