Back in 1981, in a review of the original Broadway production of “Merrily We Roll Along,” critic Frank Rich observed that “to be a Stephen Sondheim fan is to have one’s heart broken at regular intervals.” While this was often due to the emotional potency of the composer/lyricist’s songs, Mr. Rich explained, it was also because “some of Mr. Sondheim’s most powerful work turns up in shows … that fail.”