From the Playbill article -
"Stemp, Peters, and Garber will join a cast that also includes Gavin Creel, who won a Tony for his performance as Cornelius Hackl, Kate Baldwin as Irene Molloy, Beanie Feldstein as Minnie Fay, Will Burton as Ambrose Kemper, Melanie Moore as Ermengarde, and Tony nominee Jennifer Simard as Ernestina."
This seems to imply that rest of the principal cast is staying on, but that might just be speculation since we don't have any other info yet.
Caption: Every so often there was a rare moment of perfect balance when I soared above him.