Correct me if I'm wrong, but weren't the first two runs limited engagements? I think Josh Groban will be a big draw, especially among audiences that aren't avid theatre-goers but see a show or two as part of a trip to New York. Plus, there are many in New York, myself for one, who didn't see the earlier performances and will go to this show. I grant that it's not an easy sell, but I think with Groban's appeal it will at least last til the spring.
I am a firm believer in serendipity- all the random pieces coming together in one wonderful moment, when suddenly you see what their purpose was all along.