No, assuming they have a local Wi-Fi LAN. Once it is setup, you can drop the outside world connection, but there must be a local network, for the AirPlay 2 signal to connect to the Sonos One.
In fact, I’d even consider a Sonos Move instead, which they could use as a Bluetooth speaker, using that connection, instead of a local LAN. Or frankly, any Bluetooth speaker. Without an internet connection, the majority of the functionality of the Sonos system is moot.
