Probably not mandatory at all. Even when the drive train poos itself or the belts fly off or the engine quits or whatever that requires to land without power and you don't need to read far in these columns to see plenty of examples of required EOL's in both turbine or pistons.
Even twins run out of fuel or have gearboxes that seize or other problems.
The thing is the choice is yours, lower the collective and enter autorotative flight, if you have been trained to get that far and i've seen a few that haven't that tried to kill me right there.
In fact one over here in OZ recently dropped onto the ground a bit hard trying to fly without engine, killed himself.
Just remember if you haven't learnt how to do any of the above and you decide to do a lawn dart into a school, then everyone else will have to argue as to why you didn't reach the nuclear power station with the thick concrete walls to crash into or whatever.
Your widow will have to pay for the damage to the power station or the school and - we will still have to argue with someone about it - and someone will have to go clean up the mess, blood and guts everywhere and that's a blasted nuisance, wasting our good time talking to the cops all that, yessir a real blasted nuisance.
Remember when the belts fly off or the sprag lets go and the engine goes ballistic and you're sitting there fat dumb and happy trying to figure out what the noise is, there just will not be an instruictor - I should say a ****** instructor - sitting there saying auto-rotation - ready - 1 - 2 - 3 - go, or select the lever down in your own time or some other such dribble.
So yep the choice is yours, get an instructor to snap the throttle on you regardless of the type and belt it into you, with a big stick if necessary, an automatic and safe procedure, learn how do the whole bit including the touchdown or, please don't crash in my backyard.
I'm sick of all the arguing.
cheers tet.