Tim Curry, Christopher Sieber and Christian Borle have taken vacations. It seems Michael McGrath has been out recently, but I don't know if it was for vacation. I've no idea about anyone else.
I spoke with Sara at the stage door last night and asked how long she was in the show for and she said she was on vacation next week(not sure of the exact dates). She also said she'd be in the show at least through December. Hopefully she extends.