If a server goes away for good, at some point NS records will stop pointing to it. We could serve stale records as long as all of the stale record's authority chain is either still there or unreachable.
I've had an IP address from a certain cloud provider for a month. Some abandoned domain still has its nameserver and glue records pointing to the IP, and i get DNS queries all the time.
The domain expires in January. I hope it's not set to auto-renew. :-)
Note that this is already happening. The only thing my proposal would change is that it would also affect servers that used to be authoritative for subdomains of such abandoned domains. I would expect there to be very few of them: very few domains have delegations of subdomains to a different DNS server and they are larger and thus less likely to be abandoned.
