If you can get all the systems to play nice with each other, there shouldn't be any performance hit as far as I can see.  

As interesting as the idea is, I don't think there's much to be gained.  You could just as easily come up with a way to have two systems that run the whole engine, and you wouldn't have to worry about the single rotor condition unless something in the engine broke, which ain't very likely.  

Cheers,

Rusty