I think it has been controlled remotely from Sky Central for many years. (Though that doesn't necessarily rule out your point that the Millbank gallery is potentially entirely removed.)
No, the Millbank gallery is still there. It's an emergency gallery, in case of a critical issue with both primary and secondary galleries in Sky Studios at Osterley (not Sky Central) they still have a second site which can be fed directly to transmission. Sometimes pre-records are also done from the Millbank gallery.