When Mr. Abbey’s Italian company collapsed under a staggering quarter-million-dollar deficit, the Metropolitan Opera House faced a grim silence. To save the house, Dr. Damrosch and Herr Seidl staged a daring coup, replacing the familiar melodies of Rossini with the thunderous Nibelung Tetralogy. Yet, between stockholders who treated their boxes like social parlors and critics who waited for Wagner to fail, the future of music in New York hung by a single, expensive thread.