I didn't mention the Rotodyne, believe me, I can still hear it, or the tip jet helicopters of which there was a fair number because the drive was not mechanically through the gearbox.
I think 400 is right about it's continued use in the foreseeable future.
I was being interviewed in about 1975 and the board asked me my opinions on the concept of a Fly by Wire helicopter. I replied that I did not believe that it would come to pass in that century. My interviewers obviously thought that it was just around the corner so I failed in that application.
Back in 1962 as a spotty faced Pilot Officer on my first squadron, (V force) I was buttonholed by an Engineering Branch Air Vice Marshall who told me that I was in a dead end job because all pilots were going to be replaced by missiles in ten years.
They are two experts who got it wrong.