A question often asked is "Why do I need redundant DNS servers? When my services fail they don't work anyway so DNS is of no use." This is false. RFC 2182 (alias BCP 16) is about the placement, selection, and operation of redundant nameservers. You should read it. Section 3.3 in it deals with this myth:
“An argument is occasionally made that there is no need for the domain name servers for a domain to be accessible if the hosts in the domain are unreachable. This argument is fallacious.