The stresses on the rotor head and blade attachment points, TT straps, would be enormous, and the overspeed also carries on to the tail rotor, the driveshaft and bearings, the N2 turbine, hydraulic pump, blah blah.
On a Robinson, any overspeed requires a "run-out" test where the T/R driveshaft is carefully measured with a micrometer to see if it has whipped around and gone out of limits. B206 has a lot more supporting bearings, but they still would have copped it.
Hope your mate put his hand up and confessed, and didn't just hope nobody would notice...