What about the huge engine overspeed ?
Depends how quick you react. But assuming you catch it within a second (and to avoid rotor decay you would need to at least hit this target), there'll be some popping and banging before you shut the throttle.
I have a feeling that the Robinson Lycoming is so under-stressed in the cruise that it can't have any physical damage in the event that the load is suddenly removed. (Could be different in the hover where the load tends to be much greater.)
It'll be like that glorious moment I have witnessed on several occasions when some tw*t starts a Robinson with a wide open throttle.
Put it this way - the engine will be the least of your problems.
Why do you need to know?