I guess it would cause a roll. My thinking (for what it's worth as SLF) is that if the pilots were making opposing inputs, the feedback mechanism (change in pitch and, I guess, g-loading) that would ordinarily stop pilots from making full elevator deflection in high-speed flight wouldn't be there. And I suspect for many aircraft full deflection at high speed would risk damage to the stabilizer, even if the controls weren't split.
I hadn't thought about the roll, but I have my doubts about how quickly that would alert the pilots to what was happening. (If it's not clear, I'm not saying it's likely that the pilots would make large opposing inputs, or that if they did they would persist for long, just that the roll doesn't seem like it would immediately clarify the situation.)
Last edited by Chu Chu; 17th Sep 2016 at 23:50.