I would assume that they would close the show with her in it. Besides the fact that the title reads "Patti LuPone Gypsy" as if it all were one word. The show never would have left City Center and moved to Broadway if it wasn't for Patti Playing Mamma Rose. I feel that because this show is so Patti centered, it will close with her in the role as oppose to bringing in someone else to replace her.
Keep in mind that this show was revived around 4 years ago. There was no real need to revive it other then the fact that Patti was going to play Rose. It isn't really selling out because, like I said, it was revived four years ago. Maybe if there was a longer period of time between this production and the last one there might be more people who want to see it. I feel like there are a lot of people out there who have no need to see it because they feel like it was just on Broadway and have no need to see it again.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll