From 45 years of using helicopters in various roles, I only ever did 1 winch rescue (of 4 people) in a twin, the rest were all in singles. And singles don't have OEI ability, as you know.
It is not always a case of life or death. Mostly it is just to reduce somebody's suffering, and to avoid sending a rescue party into a hazardous environment. A couple of times I have winched out a person who has suffered an injury, and then refused to lift out his companions. They were able to walk out in a few hours, if uncomfortably, but the risk of 3 more hoists under those conditions for people who were not injured was too high.
Very few twin rescue machines can stay in a hover on one engine at the weights they operate at.