Even if they could be converted (and most buildings after a certain height are basically the same except for the interior) they'd likely be torn down and rebuilt; if they even can be due to zoning.
People love to hate on zoning but there are reasons for it, even if the way it's done isn't perfect by a long shot.
What missiles capable of striking Moscow does Ukraine have? It's 500km from the closest point within Ukraine's borders. That's at the limit of long-range variants of Iskander, and Ukraine only has older stuff like Tochka.