I'll run in snow up to my knees (it becomes difficult to impossible any higher than that for any length of time).

Yes, it's slippery--but so is mud, wet grass, wet rocks. You learn to push off more carefully, take higher shorter steps when there's a higher risk of slipping.

In several years of running in snow I've only fallen once--slipped on black ice. I was only bruised. Compare to five or six falls I've had running on rocks, mud, even pavement--two were twisted ankles. If you fall in snow, all you get is snow-covered!