|Wear your seatbelt|
In the normal course of operation of large dozers, one often has to work close to a face. Indeed most of the time you run one of these you are pushing material over a 'face'. If you don't have a face to push material over your efficiency goes is radically lower as the material must be pushed much further, or must be pushed uphill into a pile. Productivity in terms of yards/tons of material moved is doubled or tripled if you only have to move the material a short distance and can dump it over a face.
The down side of this is shown in the photos. D10's respond about like Wylie coyote when you drive them over the edge. When pushing over a cliff you are right up to the edge with every blade full. You can stay back a little bit in that you can leave a berm of a blade full or two along the edge so every time you come up to the edge you grunt a little and push the last blade full over and leave the blade full you are pushing on the edge for next time, but you can have the berm bigger than you can push or it doesn't work. The operator needs to stay alert to geologically unstable places (banks that might collapse under the weight of the dozer), and slick spots as well is just plain getting careless and driving over the edge. This photo sequence comes to me from Australia, and I don't know the story behind the situation, but in looking at the photos I would guess the operator just drove over the cliff.
The good news is dozers made in the last 30 years or so mostly have (by law) quite strong Rollover Protection systems (ROPS) which coupled with the modern trend toward enclosed cabs and seatbelts provide a good opportunity for survival of the operator however these events are still bad news.
The next challenge in this scenario is recovering the machine. Calling Tripple A is probably not a solution. The incline is so steep that the engine likely would not pick up oil pressure making it infeasible even if you were crazy enough to try--- to simply start it up, lift the blade and drive it down the hill. The work around for the oil pressure issue is to dump an extra 10 gallons of oil in the crankcase. Dozers are made with special high angle oil sumps, but they usually are not designed to provide oil pressure beyond 45 degress inclination. My recovery solution would require a couple large machines. Were this mine to recover, I would put a block on the back of the machine, and run a large cable (strong enough to hold the weight of the D11) from a dead man (anchor) through the block and to another D11 stationed well away from the edge of the cliff and above the dozer. With the 'block purchase' another equal sized dozer wouldn't be drug away. Then you run lines to the bottom corners of the blade, and extend them out to one or even two machines below (and far enough back---not only for safety is something falls down, but also to provide a good angle to pull the blade out of the rocks. You then yank the blade out from under the dozer and let it down the hill on the line on the back of it. Once it had moved about the length of the dozer--into the loose rock it would be level up enough that it wouldn't be the biggest deal in town to put an operator in it, start it up and drive it the rest of the way down, particularly with extra oil in the crankcase to assure oil pressure.