The chain doesn't need to be broken on a multi-speed bike, you can ALWAYS pedal backwards.
The attachment from the gear to the wheel is a "ratchet". Meaning that it ONLY "catches" in ONE direction. So when you pedal the gear turns a certain way with the wheel and this way causes the wheel to propel you forward. On the other hand, when you DON'T pedal OR you pedal backwards (or you pedal a slower rate than the wheel is spinning), then the gear is moving "backwards" with respect to the wheel, when this motion happens the gear "slips" (i.e. you get no traction).
This is why you hear a clicking sound when you stop pedaling. Because the ratchet is built kind of like a raise hook where one direction it will catch, while the other direction it will just slide up and over the raised hook (allowing rotation). So you hear the gear/wheel interface snapping back and forth over each little tooth as the wheel spins.
Edit: oh sorry, didn't read your question close enough. I always experience that when the chain came off I could pedal forward but the chain just slipped and I got NO traction, but I COULDN'T pedal backwards, the chain just wouldn't rotate...not sure what you are asking??
