After six brutal and costly months, Dutch entertainment mogul Joop van den Ende has thrown in the towel on his Broadway production of “Cyrano: The Musical.” The show will close at the Neil Simon Theater on Sunday, and may well go down as the biggest flop in Broadway history.Since beginning previews last October, the $ 7 million production, 60% of which came from van den Ende himself, suffered additional losses in the $ 2 million to $ 3 million range; two weeks ago, it grossed a paltry $ 93,000. Last week, Robert Guillaume (“Benson”) took over the title role from Bill van Dijk, who originated it here and in the Amsterdam premiere, which was a hit. But Guillaume was unable to reverse audience indifference to the show. The Nederlander Organization, which owns the Simon, immediately seized on the opportunity by canceling plans to present the Steppenwolf Theater Co. production of Jim Cartwright’s “The Rise and Fall of Little Voice” at the Ambassador, a Shubert Organization theater. “Little Voice” will instead go to the Simon, which had always been the preferred venue. The play is slated to begin previews April 15 and open May 1.