I agree with nasty_khakis and ljay. We can't really look at Peters' name alone. It's Bernadette Peters starring as Dolly in a production that earned raves, won the Tony for Best Revival and Featured Actor, and is the talk of the town. Add Mandy Patinkin, Kelsey Grammer, David Hyde Pierce, or a similar star, and I could see the show continuing to earn a profit. Scott Rudin is no fool, he's a seasoned Broadway producer, who is undoubtedly aware he'll need to advertise the hell out of the show to get through the harsh winter months. Also, comparisons to Donna Murphy's shows are moot since Murphy is not being advertised the way a full-time lead would be (though inviting critics to review her performance was a total class act from Rudin and Midler). I imagine Peters would be heavily publicized. Bernadette Peters in HELLO DOLLY is a much easier sell than Bernadette Peters in any Sondheim show.
It'd be interesting to see if the show continues to use an alternate. Midler may have set a precedent that helps attracts big names beyond Broadway veterans like Peters. If Rudin replaces Midler, it means he sees potential for this production to continue running; that means he will want to recruit a wide range of stars in the future, keeping the current model might help him do that. Hopefully once Midler's replacement is announced, we'll get word. Murphy herself may have only agreed to be an alternate for a star of Midler's caliber and for a brief run.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"