If Russia drops a bomb, then NATO immediately deploys conventional bombs with their own air force on all Russian forces in Ukraine, and China/India both sanction Russia (which basically means the whole world is sanctioning Russia, since nobody will want to piss off the USA and EU and China and India - even NK might sanction Russia).
In other words, if Moscow drops a nuke then their military and their economy both disintegrate.
If Russia drops a bomb, then NATO immediately deploys conventional bombs with their own air force on all Russian forces in Ukraine, and China/India both sanction Russia (which basically means the whole world is sanctioning Russia, since nobody will want to piss off the USA and EU and China and India - even NK might sanction Russia).
In other words, if Moscow drops a nuke then their military and their economy both disintegrate.