My phone can pre-download maps into Google Maps for offline use, I've done this in foreign countries where I didn't necessarily have full data connection. There's no reason you couldn't cache the necessary maps on the car's navigation system and let it operate based on that and an incoming GPS signal, never emitting out one bit.

OTOH, if you wanted live data, dynamic routing etc. for your convenience you could explicitly turn data on but then you'd acknowledge it comes with the caveats such as potential snooping of telemetry data.

Admittedly, I would never trust a car manufacturer to actually disable telemetry no matter what they'd promise. So, disconnecting the antennae would be the only reliable method regardless. I wonder if there will ever be a car with a physical radio kill switch like laptops.