The week between Christmas and New Year must be an exceptionally slow time in New York City. What else would explain the almost-annual P.D.Q. Bach / Peter Schickele concerts over three decades in Carnegie Hall? One particularly regrettable performance in 1989 featured a one-act opera, The Magic Bassoon, scheduled for a three-night run. The lead mezzanine-soprano, however, took sick and cancelled the third night. According to Schickele, the singer who played Shepherd “failed to show up” at the work’s premiere, and some juggling of roles and instruments was required. Coincidence? Ensembles considering mounting this operatic tale of Pan and a nymph and a shepherd and… well, be it known that Schickele has suggestions for covering any of the performers who “fail to show up.”