I witnessed a similar down hill roll happen that was attributed to an alternator. How's that, you ask?
A guy was stuck on a stump going down a steep hill. It was too slick to back up off of it and he couldn't drive over it and had no winch. My buddy was up the hill behind him. We decided to chock his Land Cruiser against against a rock (granted it was very steep), and have him hold the brakes so we could winch the other guy back a bit to get him off the stump. Little did we know, the winch vehicle had a dying alternator. I had a handful of cable being fed out to me when the engine died and subsequently lost the power brakes. The vehicle ramped over the chock and hit a second larger rock. It went up on the front left wheel and over. It did one complete roll before being save by an oak sapling that got wedged between the bumper and tire rack. That tree is the only thing that saved them from a long roll down hill and over the Jeep in front of them. No one was hurt, but the Land Cruiser suffered a bent roll cage, broken windshield, damaged hood and all four corners. Just goes to show how important the little things can be. Since then, almost all of us that ride together have gone to manual brakes and I guarantee he keeps a closer watch on the gauges.