As mentioned by SND, if the engine fails then it is already shut down.
A PT6 failure I had (turbine let go) resulted in such a plethora of captions on the CWP that it was a case of fly the aircraft, read off the failure warnings and finally notice one row of engine gauges at zero. Oops!
Winding off the wrong throttle didn't even enter the equation as a single pilot operation. But I have had a very experienced pilot in the LHS retard a PCL before I had verified the call, fortunately without creating an issue at the time. Salutary lesson
