This was my concern, can this happen while driving? And is there any backup safety mechanism if break or fuel pipes go off while driving
I think it can happen any time - the brake pipes weaken, then under the extreme pressure of the brake fluid when braking, it bursts.
The experts here will be able to explain it better, but my understanding is the the design of the brakes puts the front and rear brakes on different circuits, so if one fails the other should still work. But once you have a leak in one, it all deteriorates, you will lose fluid, your pedal will eventually fall to the floor and you'll lose them all. Obviously if you have a brake master cylinder failure, you will lose front and back at once.
Mine went after the car had been standing a while and the leak was at the back. So the fronts still worked for a short while, but it was obvious there was a problem when braking.
The handbrake (traditionally, anyway - dont know about these fancy electronic handbrakes) is mechanical -its on a cable and doesn't use the hydraulic brake lines. So in a complete failure, thats all you have left. I was always taught that if the brakes went, slow down on the gears as much as you can then use the handbrake to bring it to a complete stop. Low range was handy in the ML because it increases engine braking so you put less strain on the handbrake. Only for emergencies though obviously!
I think if your fuel pipe went, you'd end up with engine warning lights as your fuel pressure would drop. How much warning you'd get depends on the failure I suppose.
Brake pipes on the ML lasted 17 years