The Yankees victory celebration yesterday was even sweeter for co-owner James Nederlander after a hardhat with a heart returned his lost 1978 World Series ring. “Great, isn’t it? It shows there are a lot of honest people in the world,” Nederlander, 87, told The Post’s Chuck Bennett. Alfredo Blanco, 43, saw the $15,000 ring sparkling in the parking lot of Mirko’s restaurant in Water Mill, LI, early Monday morning. The night before, the diamond-studded treasure, inscribed with “Greatest Comeback in History” and Nederlander’s name, had slipped off his finger. “I thought it was gone forever,” said the prolific Broadway producer. The next day, Blanco called to say he found the ring and wanted to return it. Last night, the two met at Nederlander’s Southampton home. No reward was necessary, Blanco insisted. But grateful Nederlander promised him and his family some of the best seats at the Stadium next season.