Technically Millie is a flop since it did not recoup its initial investment, but we may need to invent a new term for a show that does run for a time and yet does not return its nut. It could lose all of the investment or only part, even a small part of it, and it is still a flop.
This list which gets longer every season includes: Shenandoah (the first show to run over 1000 performances and not pay off), the original Chicago, Tommy, Kiss of the Spider Woman, Ragtime, Sunset Boulevard, Jekyll & Hyde (the current long-run non-payoff champion at 4+ years), Sweeney Todd, and now Millie.
The 1975 Chicago, Purlie, Raisin, Coco, and Shenandoah did eventually make their money back on a post-Broadway tour.
Some flops with short runs and good reviews are called a "success d'estime", but that term is used for an arty show with fairly good reviews that fails to find an audience like Side Show or either production of Jumpers.
Is "long-run, non-investment-returning production" too long a term?
[N.B.--Wicked has not paid off nor will it for a while. The show cost 14 mil to open and even with million dollar plus weekly grosses, that will take well over a year to get into the hit column.]
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--Carrie Fisher