The dashboard has nothing to do with data collection. That happens internally with various chips and ecu. The data being sent to the company servers don’t care about your dashboard, that’s handled by a different chip that has 3g/4g connectivity. In fact, you can buy a fancy tool that plugs into your obd II port on one end and a laptop in the other see real time data about how various systems are performing and what’s happening based on your driving.
I don’t know if 3g is completely dead at this point but it’s on it’s way out. I think those on-star enabled cars are using 3g but I could be wrong. As far as ripping those out, I doubt it since all of that is integrated into a single chip or it’s soldered on. Best that you can probably do is hope that it is relying on defunct network so it can’t communicate to the mothership anymore but you wouldn’t have a way to verify that.