If I ever got a car with On*Star spyware, first thing I'd do is take a pair of hedge clippers to the antenna cable. Spyware in my car that can't be turned off and that can turn my car off or unlock it remotely? No fawking thanks.

To answer your question, On*Star only uses satellites for GPS signal. It gets its internet/WiFi connection through the cellular network. If you exceed 90 days, you'll be paying to essentially duplicate the functions that your cell phone can do. (Interestingly, most phones these days have accelerometers, so they could even be set up to call 911 in case of a car crash.)

So if the WiFi works in your vehicle at your cabin, you should be able to find a phone or hotspot that talks to the cell network and provides the same level of service. The cost and latency of satellite shouldn't be needed. New On*Star vehicles apparently use AT&T, so I'd try to find a modern hotspot that uses their network and experiment at the cabin.