It's more a near-miss than an accident, but here we go:
We were coming back from holidays with my dad, he was driving and I was riding shotgun. We were on the highway (middle lane to be exact) when the car in front of us suddenly lost speed, brake lights still off. My dad was able to narrowly avoid the car, it's frightening to think that we probably owe our life to his reaction time. To this day we have no idea what happened.
Could be that both taillights / brake lights were out. Seems super unlikely, but I have seen someone driving on the highway with both taillights burnt out, headlights on.
Probably hard to realize they're out until someone lets you know / pulls you over.
Hum, I never considered this option, though a bug in the CAN bus is more likely than brake lights being out. Some Renault cars were notorious for this, but in this instance I believe it was a Volkswagen Touran.