DURING LANDING ROLLOUT, THE LEFT MAIN LANDING GEAR LEFT THE RUNWAY. THE AIRPLANE RETURNED TO THE RUNWAY, VEERED TO THE RIGHT, AND EXITED THE RUNWAY ON THE RIGHT SIDE. THE AIRPLANE THEN IMPACTED A DITCH AND SLID TO A STOP ON THE TAXIWAY. THE LEFT MAIN LANDING GEAR SEPARATED AND THE NOSE GEAR COLLAPSED. THE PILOT STATED THAT THE WINDS VARIED FROM CALM TO A 90 DEGREE CROSSWIND IN EXCESS OF 20 KNOTS.