I still like Seth's system-autodeath, but it's been retired for a while
now.
From the summary:
system-autodeath is a cron job that runs daily, checking the current
time versus a configured death date for the machine. Within one week
of this date the system will emit log notices to syslog.alert notifying
that the system will remove its default network route on a specific date.
On the date the system will have its default route deleted. It
will continue to do this every day until someone does something about it.
really anything we do though is going to be invasive and unwelcome to
some.
kevin