To book a Broadway theater these days, you either need a movie musical, a movie star, or Idina Menzel. The two promotion companies that recently took over D.C.’s National Theatre are betting that the one-time Wicked Tony winner can pack the National for five weeks this fall, and then take Manhattan next spring. Menzel will star in If/Then, a new musical from the creative team behind Next to Normal. I don’t know much about the plot of If/Then, other than Menzel will play a woman on the cusp of turning 40 who returns to New York and reunites with old friends, some of whom will be played by Menzel’s old friends, including her Rent co-star Anthony Rapp. That sounds like a season of love, so start counting the minutes untilIf/Then opens in early November.