I had an 80 series do a front right brake line, while I was waiting for the winch to be connected to pull me up. Reversing down hill with only 3 brakes active till you possibly bleed out is terrifying, but I engine braked all the way down. The 80 made it home after blocking the broken brake line. Scary as hell sitting on a steep incline knowing you have stuff all brakes. I did have it in first gear, low range, and handbrake on at the time the line let go.My son sent me a recent youtube clip, similar to your experience, think an 80 series which he had in 4 wheel drive.
Got 2/3rds way up and still came down backwards, luckily he kept it straight but still was a whiter shade of pale
so even in 4 wheel drive you can end up with the same result