Composite structures for aerospace applications are designed with the assumption that the structure has already sustained "Barely Visible Impact Damage". BVID is usually defined as damage that can be seen visually from approximatley 5 ft away. The structure must be able to sustain ultimate load with BVID and no growth of damage through the fatigue life of the aircraft.
Damage that's greater than BVID obviously must be repaired, but again, the structure is designed to sustain limit load with visible damage and two inspection intervals.
As for repairs, composite materials isn't all that difficult to repair, just different. Generally the damaged area is cut /scarfed out and replacement plies bonded in place.