As I mentioned before, I would be more disturbed by the loss of Russian architecture than by the people who might die if the Kremlin were bombed out of existence. If Putin has indeed holed up in a bunker beneath the big red building, the appropriate response for him firing nukes would be to make a big hole where that building stands. Not with nukes, just big, conventional bombs. I don't think their military would be able to defend against the US alone, certainly not the US AND Nato/allied countries.
I just saw that 13 AN124 aircraft were arrested, mostly in Canada. This means the crews must de-plane and the aircraft must stay put. That also means Russia will have a hard time moving large amounts of, well, anything.