The unsold ones go & live out their remaining years in obsolete racquet retirement homes, where they're occasionally visited by the current models and taken out for a gentle hit once a year at Christmas. But they have to be back before 6pm ready for lights out.
Sometimes though, they just die and the good racquets go to Racquet Heaven where they're played with by angels and saints. Sometimes God gets his Barricades on and has a run around too. But, if they've been bad ......