The new production by director David McVicar, which opens at the Met’s New Year’s Eve gala, has already lost its original star tenor (Jonas Kaufmann) and soprano (Kristine Opolais). Now its planned conductor, Andris Nelsons (Opolais’s husband), has withdrawn as well – and he’s being replaced by a maestro who is certainly available and knows his way around the house and the score. (But with Levine’s fragile health and this production’s bad luck, we can only hope he actually makes it.)