Gone was Leonard Slatkin, who presided over Monday night’s season premiere of the Verdi opera with a striking lack of coordination between the orchestra and singers. In his place Saturday night was Met mainstay Marco Armiliato — only four hours after he had led a matinee performance of another Verdi work, “Aida.”
I've never heard of this happening; a conductor simply removed and replaced. Leonard Slatkin was originally hired to conduct Corigliano's "Ghosts of Versailles". But when the Met decided it was too expensive to produce, they substituted "Traviata".