Was Rannells not working? Not selling tickets? Seems like a pretty speedy replacement.
Rannells always had a very short contract (http://www.playbill.com/news/article/andrew-rannells-steps-into-the-high-heels-of-hedwig-and-the-angry-inch-aug), though not clear if that was his choice due to other commitments or the producers wanted to see if there were other/better options.
The commitment (no intermission, no understudy, 8 x week) is a lot to ask of a working TV actor, so I'm guessing he opted not to do a longer run. I saw NPH back in May and was kind of stunned that he was doing that intense of a performance for 5 months without much of a break in that timeframe. It's such an amazing show.I will say that the AR shows have not sold out the way the NPH shows did. Granted, it's not summer anymore, but I had to get my NPH tickets for a May show back in November. I'm seeing Andrew Rannells this Sunday and I bought those tickets just last week, and they are better seats.