Per a recent email exchange with Aaron Spangler, who asked me to enter this
faintly feature-request-ish bug; I'd assign it to him if I knew the account he is
in bugzilla under...

In the event of LDAP being inaccessible for whatever reason, there would be value
in having some form of backup capability within sudo - a timeout, perhaps - after
which sudo may look for a local sudoers file and use that. Of course, if the code
to make it work with nsswitch.conf were in place, then perhaps that would work
as well (e.g. "sudo: ldap files" in nsswitch.conf) though the failover might not be
what is desired by all... it probably needs to be optional behavior, at least as a
compile time option if not a run time configuration option, as someone is bound
to object one way or the other...