They're embedded on the Z30 it appears so hopefully not for me. The classic has the hard back if I remember correctly so with enough wear I could see it happening. Then again my 9700 has seen it all but the logo never fell off so maybe not.
Some passport users have had the bad luck of them falling off. Though I don't think it will happen to most, and if it does, it's a chance at getting a warranty replacement.
Don't think so, they look quite sturdy to me. Moreover I feel that it's a solid plate inside and the back cover has the logo cut out on it rather than individual pieces put together.