Or to stick with a self-contained-within-your-own-original-script approach...

Have your daemon note which network-interface it used last.   Then before each subsequent iteration, check to see if that same interface is still up.   If not, have the daemon bounce itself.   Of course you'd need some delay or counter or somesuch to avoid flapping.   Or else use an interface that *is* up, perhaps from a configured list of permissable interfaces.

You may find it necessary to think "ip address" instead of "network interface", depending on implementation.

Searching CPAN and searching The Monastery on "network interface" turned up some potentially relevant hits.