It belongs to CBS, and it will continue to be used for the show. It is a venue of monumental historic significance to TV and I doubt they would ever part with it. Plus I don't think it would work as a legit theatre any more, at least not without a huge expenditure.
They are contractually obligated to return the theater to its original layout owing to it being an historical landmark. IF they were to ever give up using it as a TV studio.