After practicing maneuvers, autorotative approaches, and landings in the local area, the flight instructor and the student pilot were practicing autorotative landings from a hover following a simulated loss of engine power, off-airport, and over sandy terrain. While hovering about 3 ft. above the ground, the student pilot reduced engine power to enter an autorotation. Between 1 and 2 ft. above the ground, a gust of wind struck the helicopter from the right that resulted in the helicopter rolling and drifting to the left. The flight instructor then took control of the helicopter, but the left roll and drift continued, the left skid impacted the ground, and the helicopter experienced a dynamic rollover onto its left side. During the rollover, the main rotor blades impacted the ground and the tailboom and main rotor mast pylon were substantially damaged. The flight instructor reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operation.