If a foamie hits the main rotors, it will take a couple of big cuts. But cuts in foam are easy to fix if the rotors don't hit anything else.

However, even hitting foam will almost certainly destroy the heli on the spot. I could easly see the rotors putting a couple minor cuts in the foam, the foamie flys off, while the chopper with it's now bent up mainshaft and messed up rotors now thrashes itself to death on the way down, where the ground finishes the job. It would be a heck of a crash on video, that's for sure.