“The Amato Opera is as far from the Metropolitan Opera as high school hoops are from the N.B.A., but it is a beloved part of the constellation of small performing-arts companies in the city.” Its impending closure after 60 years is a product of that smallness, as director Anthony Amato, yearning for retirement at 88, “said he had decided to shut down the company because he feared its quality would suffer without his dedication.”