As for Patti, it's not my idea of good casting anymore, but I'd be interested in seeing her do it... I think it's better than her casting as Joanne! (ohhhh! But kind of mean it)
And I really wouldn't be surprised at all if she wanted to step in for a month, it's a juicy role that fans would probably LIVE to see her in, it would bring it new buzz for a time, and I bet the producers would go for it.
I'd actually like to see what happened if Bernadette went into it as The Witch ... she looks amazing, sounds good, and broadway fans would go crazy.