My personal philosophy - I can handle a weather-related bike crash (although the older I get, the harder the ground gets!) ... but I CANNOT handle crashing, and then having an out-of-control car roll over me!
If it's slippery enough to be treacherous, and I can't physically isolate myself from HEAVY traffic (by riding on sidewalks, dedicated paths, etc.), I'll find another mode of transportation for that day. The stakes are just too high.
Far as ice riding... no sudden moves. Straight over the ice rink, anticipate the bumps and go over them GENTLY. Be prepared at all times to dismount or take other measures. Happy to say I haven't crashed due to icy conditions in almost 2 years / 10,000 miles.