Engine-off autorotation, same thing, in the last few seconds as you adjust your touch point, you will find yourself flying with the rotor decayed to its absolute limit of lift vs RRPM
But you are not transmitting Tq through the MRGB to keep the rotors going - it is an entirely different scenario to the one first postulated.
If you let a student decay the Nr to 40% - or anywhere near that - you should give back your instructor ticket.