As of 15 Feb 2022, disabled accounts on Joplin Cloud will be automatically deleted after 90 days. A disabled account is one where the Stripe subscription has been cancelled either by the user or automatically (eg for unpaid invoices).
Although it is an automated system, I will manually verify each account that's queued for deletion over the next few days for additional safety (for now everything's working as expected).
When an account is queued for deletion, all notes, notebooks, tags, etc are removed from the system within 2 days, and permanently deleted within 7 days. User information, in particular email and full name will be removed from the system within 2 days, but archived for an additional 90 days for legal reasons, after which they will be deleted too.