There are thermostats, among other things, that use standard protocols and still work in a “dumb” way if not connected. You just need to do some homework.
The thing in the article is a thermostat-zone controller system, where the tablet is part of the multi-zone controller, and there aren't really separate thermostats.
In the US, it's common that the input to each zone controller is just a open/close contact, so in the worst case you can call for heat by shorting the right wires together.
I have a smart thermostat that I use the provided app to control, but one of the reasons I went with it is that there's also an http server in the device firmware that can be used to control it (so if they totally ruin the app or turn off the server or whatever, there's a way out).
