In all my years of driving complete beaters in awful road conditions, I’ve never encountered a mechanical failure that was that dangerous. The closest would be when I had a strut snap and punch a hole in my tire while driving down the highway. But even that didn’t wind up being particularly dangerous. I still had way more than enough control to just make a controlled stop on the side of the road.
The only mechanical failure I can think of which doesn’t always just allow you to make a controlled stop is a busted brake line or master cylinder. But a lot of times that will still result in a slow enough loss of braking capability that you still have time to make a controlled stop before your braking ability is gone. Everything else that I can think of will render the vehicle completely undrivable before it breaks in significantly dangerous way. Of course that doesn’t mean that things won’t break in a far more expensive way if ignored.