To be clear, I have concerns with two things: single sensor array; and Tesla confidence to solve autonomous city driving (regardless of the sensor array).
Winding mountain road is much simpler scenario than driving in the city. Given the fog (which disables the camera), radar (essentially, a single pixel camera) will be superior in detecting obstacles. Usually, winding mountain roads will have guardrails, i.e. obstacles that determines the road boundaries. Either multiple radars or (I hope) object persistence will be able to form a 3D picture of the road (phased radar arrays are out of reach ATM, although there is some interesting research in that space). So, without reliable feed from the cameras, relying on the radar(s) only the car should be able to more or less “figure out” the road and avoid obstacles. There may be a way to detect the lane divider (more reflective than asphalt at lower frequencies?) but I have not heard of it. IR sensor can definitely do that and other manufacturers use them. So, a combination of radars and IR should be able to drive you in complete fog.
Going back to the multisensor array. It may be more expensive but its capabilities are much superior than single sensor array.