I’m not sure I follow. Does the thermostat become otherwise unusable if there’s a network outage?
https://www.nytimes.com/2016/01/14/fashion/nest-thermostat-g...
I've actually found that I keep the temp at a specific one for the season so I've never actually needed any of the remote features except I like the fan scheduling thing.
I thought I would do the whole preheat or cool the house thing and what not but it's actually not a relevant feature for my local climate and house.
So I found that it's way better just to leave the thermostat on and maintain the conditioned or heated air.