maybe non-volatile e-paper, which can be updated easily if things are up, and if the system is down it still works as well as the printouts
Technologically it seems doable. Big enough order brings down the costs.
https://soldered.com/product/soldered-inkplate-5-5-2%e2%80%b...
Of course the real backup plan should be designed based on the actual needs, perhaps the whole system needs an "offline mode" switch. I assume they already run things locally, in case the big cable seeker machine arrives in the neighborhood.