Do IDA annual subscriptions allow for an IDB file to be reopened years after it was created, even though I do not have a subscription for IDA anymore?

Yes, you can still reopen an IDB file with IDA even after your subscription has expired. Any version of IDA obtained through a subscription will always allow you to open and read files created with that specific version. However, without an active subscription, you won’t be able to make changes or save modifications.