The difference between RWD and FWD is not nearly as large as it used to be.
Back in the day, the biggest risk with a RWD vehicle was that the front wheels would stop turning altogether when you applied the brake. Then you'd have no steering control, and say "hi" to the snowbank or the car in front of you. Modern ABS systems really do eliminate that problem.
The other big problem was the rear wheels slipping. Accelerator + black ice = spinning car, guaranteed. Years ago I got surprised by black ice while accelerating on a highway ramp -- at night, no street lights, I thought it was dry pavement. I did 2-1/2 donuts then pulled out of it going backwards at 70 kph. Luckily I stayed on the road and was able to stop safely.
That sort of thing simply won't happen with a Tesla; the traction control is astounding. I've taken a Roadster with summer tires onto a snowy road and floored it. The car accelerated gently, gracefully, and with no drama. Same thing when you lifted off; the regen gently decelerated the car. It was a thing of beauty.
Give the above I'm certain the RWD Model S will have no problems whatsoever driving in winter conditions. I wouldn't let that hold you back.