As a matter of practice, before removing an authoritative name server, we would usually point it to another server. I.e. ns3 might now point to ns2 and we'd Le

As a matter of practice, before removing an authoritative name server, we would usually point it to another server. I.e. ns3 might now point to ns2 and we'd Leve that for a few days as not all caching is respected. After that you can remove the server and the name and if it's cached somewhere, it still points to a valid server.