Because you asked, I will report that at the invited dress rehearsal of the '92 "Guys & Dolls," Carolyn Mignini stuck out like the proverbial sore thumb. She looked too old to be playing opposite Peter Gallagher, and got a tepid response throughout, particularly at the curtain call (where, of course, Faith Prince was cheered to the rafters).
So it did not surprise me at all when it was announced that Mignini was out as Sarah.
That is not to say that they wound up with a first-rate new Sarah; Josie de Guzman was only okay, and I've seen any number of superior Sarahs (Anita Gillette, Julie Covington, Ernestine Jackson, Jenna Russell). But Josie de Guzman was appealing and her scenes with Gallagher did come to life, even if it was mostly Gallagher that carried them.
Would the production have succeeded the way it did had Mignini been allowed to remain? Yes, perhaps, but I think critics and audiences would have found Mignini lacking, while Josie de Guzman was sufficiently winning as to not disturb the overall cheer of that production.