Katie Holmes’ Broadway play just closed because of faltering ticket sales, but she and her co-stars certainly aren’t suffering any shortage of fans. A huge group of admirers gathered outside the Music Box theater on Sunday night to say farewell to the cast after their final performance. The crowd grew so large, an insider tells Page Six, that the NYPD advised the entire cast to exit through a back entrance for their safety and that of the crowd filling the sidewalk. And while some were disappointed not to get a glimpse of fan fave Holmes, Tony Award winner Norbert Butz and star of stage and screen Judy Greer, the insider reiterates, “It’s what the NYPD advised the entire cast to do.”