As far as we know, the interludes are meant to be used while they are trapped inside the room and cannot leave and feel like songs that never start. But, assuming the musical follows the plot of The Exterminating Angel, they are able to leave once they re-ennact the situation that got them there. Now, Cameron Mackintosh on the article about the famous call were Sondheim played he score, said that was missing was a Loveland-style sequence that he had not written. Now, that "reenactment" at the end seems like a perfect fit for a Loveland sequel. Maybe we are getting both, the interludes and re-constructed version of the solos Sondheim might have sketched for that section.