TheBigA said:
I was thinking the exact thing when you said the pre-Conan Leno studio was empty. If I remember correctly, that portion of the building was added on, and wasn't well built. If it's not being used, it's probably ripe for demo. At some point even Leno will have to move. I think they have to amortize the costs of the studio he's in.
The pre-Conan Leno studio was Studio 1, one of the two mirror-image studios on the Alameda Avenue side of the building. As the number might indicate, it was part of the initial core of the complex circa 1950-whatever it was. (The current facade was added on later, including the area that was used as the Leno audience lobby.)
The adjacent studio, 3, is being used for Access Hollywood.
Those are still good, useful studio spaces in a great location. I suspect they're less likely to be demolished than to be adaptively reused by someone other than NBC.
Unless some things changed since I was there last, I think this is reversed. Johnny's studio was Studio 1, which is now Access Hollywood. Leno originally used that studio for "Tonight" before moving to Studio 3 a year or two into his run, before moving to Studio 11 for The Jay Leno Show/Tonight.