Clinton,
With all due respect, you are asking for an answer to a non-problem, there is no answer to the question of: Is the throttle mechanism in its entirety more likely to fail in the idle position than the mixture control fail in the idle/cutoff position.
One thing is for sure, you will get the power back faster by opening the throttle than you will getting the mixture out of idle cutoff.
Not reducing an engine to idle at all, and then only slowly, has serious benefits for turbo-charged engines ----- another very important reason for very slow throttle movements on the "bigger" piston engines is to preserve the balance weights in the crankshaft, jambing or worse, losing one of the balance weights will do very serious damage to the engine ----- including in once case I witnessed at YSBK, venting the crankcase in a way never intended by the manufacturers --- resulting in an engine fire. The engine was an geared turbocharged 520 or 550, what a mess, what a bill, over $100,000 including airframe repairs.
Be very very gentle with the throttle, only move the mixture to idle cutoff at idles, or if called for in a real emergency.
The issue of control and what happens if you get below Vmca is the same, regardless of the type of engines.
In all the years I have been flying, twice I have had throttle problems ---- the spring that moved the throttle open saved me both times ---- one was a cable break ( Cessna 205 ), the other was a linkage dropped off, DH 82A ----- no split pin through a nut.
At least one thing you can do in four engine aircraft, whether it is a Heron, a DC-4 or a B707, is that you can pull back a symmetric engine to regain control ---- temporally eliminate the control problem ---- if you have the height. I have only demonstrated this on a Heron and a B707.
Tootle pip!!