The prop is not going to rotate backwards when the engine dies... unless it stops just short of TDC, and compression pushes it backward.

Put a prop on a dowel or screwdriver that allows it to turn easilly. Aim the prop into the wind. It will NEVER turn backward without you pushing the blades and forcing it. (but it might spin fast enough to develop enough "blade lift" to pull itself forward...)

The reason some hand cranked engines in the 1920's and 1930's could be restarted in air was the prop "windmilled" forward.