WRT the temperature as such, I’ll happily ride in any temperature I’d consider skiing or skating in. Or doing yard work in. Not a big deal once you’ve gotten your clothing needs dialed in. My bail-out plan in case of something unfixable is simple. I ride from the suburbs into the city. I’m never more than perhaps a mile away from some sort of public transport. I carry extra clothes that can keep me warm while waiting. And a sturdy lock to hopefully keep the bike secure until it can be retrieved. Calling a cab would probably work too.
Through the suburbs there is a bike path just about all the way. Once I hit the city, traffic is so heavy that the speed difference between me and cars isn’t much of an issue any more. I use high-count, studded, deep-tread tires. They roll heavily but will deal well with ice and hard pack with only a little care.
WRT car behaviour my impression is ”the worse, the better”. At bicycle speeds, it takes nearly a blizzard before visibility is affected. At car speeds, and car headlights, the backscatter gets so much worse. Traffic slows down, and drivers become more careful.
The only thing that will definitely keep me from riding is snow depth. 3” or more, The commute simply takes too long, becomes too tiring. High winds have caused me to cut the commute short, not out of strict necessity, but rather in an attempt to be sensible. Those issues I’ve had have been mainly self-inflicted, ie unwillingness to use the bail-out plan even when available.