The Hiller UH-12 POH actually mentions “Emergency Exit in Flight” as an emergency procedure. What emergencies would make the pilot do this and why don’t other helicopter POH’s mention this?
One example of a helicopter bailout that I am aware of was the ditching of a USAF Sikorsky HH-60G during the infamous "Perfect Storm." After several failed attempts to refuel from a tanker in the extreme weather the pilot decided to ditch. He hovered to allow the other occupants to bail out, but he was unable to bail out himself as the engines flamed out from fuel exhaustion and he autorotated to the water. After it hit the waves it rolled over. At this point he realized that he had not jettisoned his door as per the procedure for bailout or ditching so he was trapped. He managed to escape, but one of the other crew was lost at sea.