Dick,
there is a whole lot of risk analysis sitting behind most of these operations both from a down the wire people and the hopefully still flying crew. As has been stated try and find a twin that will fly on one engine and they are pretty rare at the weights usually found in OZ.
Single engine winching has a long and safe background in NSW with more than 800 training and real winches done in single engine per year. One particular " consultant" believes in twin winching only yet other agencies have a safe history over many years.
Keep in mind a stretcher carry over a long distance or a walk in can expose a number of people to risks of falls, trips etc.
Want to discuss winching with or without a ballistic cable cutter? That should chew up a few pages. Start with over land and over water.
