Remember - engine fails.......pause, 1 second, two seconds for real world reaction times - where is your Nr now in the fast cruise at 14 degrees of pitch???? decaying very, very rapidly!
I think this is an important aspect in this discussion.
While theoretically cyclic back will be an effective means of keeping and restoring RRPM this will only work in a certain AoA range. With the collective in your arm pits you will likely see a significant decay in numbers even while in cruise flight.
That said the same will happen if you leave the cyclic fully forward and just drop collective. You will unload the disc and not get the necessary upward flow through the disc. At least not until a very high RoD builds up at which point the NR may already have dropped below PONR.
In Autogyros this is a frequent cause of fatal accidents:
Push the cyclic forward a bit too agreesively, watch the rotor NR decay in 1 or 2 seconds beyond PONR and drop with a stopped rotor from altitude, even with your engine in the back still pushing.
So both actions have to happen. Relax cyclic, lower collective.
You can discuss to which extent you do what but failing to do one of the two will likely end in tears.