The instructor reported that his student was taxing the helicopter in a north direction along a taxiway parallel to runway 12/30 with a near direct tailwind of 10 knots with gusts to 19. The student started to lose tail rotor authority over the helicopter. At this time the instructor took control of the helicopter and proceeded to apply full left pedal until they regained tail rotor authority and directional control. Because of the strong winds from the south, the instructor opted to keep control of the helicopter until they were airborne and he proceeded to continue their taxi to the displaced threshold of runway 12. Upon reaching the displaced threshold, the instructor started a 220 degree turn to the left in order to line up with a takeoff direction to the south into the wind. The instructor reported that half way through the turn the helicopter violently yawed to the left, and he applied full right pedal to cancel the yaw but was unable to arrest the helicopters left yawing moment. The helicopter landed hard on the skids, damaging the main rotor and severing the tail boom aft of the tail rotor blades hazard guard and before the tail rotor transmission. The pilot reported no mechanical issues with the helicopter prior to the flight. The wind limitation listed in the Pilot's Operating Handbook for the helicopter is 25 knots including any gust factor.