Winter driving is really no different from any other kind of driving in which the driver exceeds the limits of the vehicle's available traction. The methods of recovery are mostly well-known; the problem is more often the driver's inability to implement them in a timely manner.

Constant input from wheel speed and accelerometer sensor arrays, coupled with the vehicle's ability to individually brake/slow wheels (which also gives the vehicle the ability to accelerate individual wheels independently!) means that it could be a far easier 'problem' for self-driving cars to solve than it is for humans.

Again, if they're working on it :) But there's already been decades of work put into ABS, traction/stability control, etc.