NEW YORK — “Mamma Mia! The Party,” which you can see in London, is one thing. John Kander, Fred Ebb and Joe Masteroff’’s masterpiece, especially as enshrined on Broadway in a searing and unforgettable 1998 revival starring Natasha Richardson and Alan Cumming, is entirely another. “Cabaret” is not a high-priced bacchanal; it’s Broadway’s greatest cautionary tale about the dangers of letting a party inure you to a fascist takeover. So, sure, go ahead and persuade an audience to arrive an hour early so they can imbibe Moët & Chandon and $29 cocktails in multiple new bars, funnel them through an...