All right, how do you make internal site communications completely
oblivious to a change in your externally-visible routing prefix?
You declare that any app that keeps connections around for more than
some time period T (say for 30 days) have a mechanism for
detecting and recovering from prefix changes. That solves the
problem for all apps, not just for local apps.
Ah, well, if we're allowed to solve problems by fiat, let's just
declare that everyone "do the right thing" about site-local
addresses, automatically drop unauthorized packets, end hunger and
violence, and brush their teeth.