I lived in Lake Tahoe for six years and drove AWD, FWD and RWD vehicles. Everyone one focuses on "going", but the MS is a very heavy car and all the bad stuff happens when you're trying to stop or turn. You can get stuck if you can't go, but you probably won't get into too many accidents. I lived in Alpine Meadows which has a long descending road with a series of turns in a meadow before it reaches the highway and on the first major snow of the year those turns would be littered with cars that slid off the road. And these were full time residents, people who should know better.
No matter whether you have all season tires, snow tires, studded snow tires or chains it's really important to slow down dramatically compared to dry pavement driving. If you wait until you've lost traction to think about slowing down, it's too late. All vehicles become toboggans at some point and then you're no longer the driver, you're just along for the ride.
I also suggest turning down the regen if the conditions are difficult. The last thing you want to do in marginal conditions is hit the brakes and the full regen is like hitting the brakes unless you modulate the "go" pedal very carefully. Driving on snow/ice might be time to recall how to gently use the brake pedal.
To the OP's question, California has levels of chain controls:
- Chains or snow tires (any tire with M+S on the sidewall)
- Chains or AWD with snow tires
- Chain only (you really don't want to be out in these conditions anyway)
So yeah, buy a set of chains, you never know when the CHP may require them on your RWD MS.
