This is all just seems like a desperate attempt by the producers of the Tonys and Hello, Dolly to give themselves more attention and try to "create suspense." Let's face it, if Bette doesn't perform, the Tonys will be a lot less exciting - not to disparage any of the other shows that will be performing, it's just Bette seems like the real "event" performance. This is all just PR horse****, and after the Tonys, we'll all probably feel foolish for being so angry about it.
That being said, if she doesn't perform ,and the show were to lose one of the awards, it probably would be Best Revival to Falsettos or Miss Saigon (i'd prefer Saigon but if Dolly loses, Falsettos definitely takes it). However, Bette does seem to be an absolute lock for Best Actress, just based on not only the odds but the general critical and voter sentiment. I think maybe Eva or Christine could pull an upset, but since both their sows got so few nominations, it seems unlikely (I'm exlcuding Patti and Denee because Patti's last win was more recent than Christine's and Great Comet is definitely doing to sweep the technical categories).