Remarkably, La Scala is reopening this week on time and within budget. It looks good, and the good acoustics have survived. “Continuity is the leitmotif of Tuesday’s gala. The work chosen to reopen the theater is Antonio Salieri’s “Europa Riconosciuta,” the opera that inaugurated La Scala, in the presence of Empress Maria Theresa of Austria, on Aug. 3, 1778. Clearly, the intended message is that La Scala is both modern and eternal. But now that the dust has settled, it’s worth asking if the closure and the reconstruction were actually necessary.”