The simulator also works to practice the procedure. It's also easy to practice with a real one. Start out by hovering maybe 2-3 meters, shut down power and learn how to manage the collective to get a nice soft landing using the stored energy in the head. Every helicopter has a "dead man's curve", which is a zone where you cannot use energy stored in the head like you can at 2-3 meters, nor are you able to build or maintain headspeed from a hover to make a soft landing. Any helicopter can be landed in autororation in forward flight at any alttiude. But not from hover in the "dead man's curve".
So the next step after you master collective management at 2-3 meters is to start flying the helicopter around and learn how to use the flare to build headspeed and stop the helicopter prior to touchdown. This can be practiced at much higher alitude and use the "bail out" feature until you get proficient at it.
You will very quickly learn to land into the wind like a fixed-wing does. And will quickly learn that if you get a rotor stop it is impossible to get it going it again (use the bail out).
For autorotations in a real emergency the ArduPilot system will try to maintain altitude if you get a power failure in flight. So the autopilot will simply stop the rotor in any of the altitude controlled flight modes. And then you have a problem. Fortunately, there's usually some sort of indication that a power failure is imminent. I've had to do two of them on commercial flights, once when I blew the clutch in my piston heli. Another time when I had a bearing go out of the motor in my electric. It was the audio feed on my FPV that alerted me to both before the headspeed alarm went off on my radio. In a real emergency you got a lot of stuff you're watching, not expecting a loss of power situation. So you have only seconds to get the heli out of auto or loiter and into Stabilize to save it. I've gone to setting up my Stabilize collective pitch curve (the IM_STAB_COL settings) so the stick at bottom is -2 to -3 degrees of collective pitch. That way it only takes flipping one switch to get back into Stabilize and bottom the collective immediately and it's automatically at the right pitch to save the headspeed. Then, once you get a forward glide established you can feather the main rotor and get a better glide ratio. If you auto straight down she's not going to float very well and she'll build a lot more descent rate than if you get the heli into a forward glide. So setting the Stabilize pitch curve eliminates the "guess work" when you only have seconds to react.
In a real emergency in hover from anywhere to about 4-5 meters to about 12-15 meters you're in the "dead man's curve" with a heavily loaded UAV heli. Altitude is always your friend if you're going to split the needles in flight with a helicopter, either intentially or unintentionally.