The only reason the vast majority of the Russian civilization and populace would survive and continue is because China has such a small nuclear arsenal (~230 warheads, including both deployable and non-deployable) and only 66 ICBMs with the range to even reach targets in European Russia. Russia, on the other hand, could end China many times over with its current stockpile of 8,500 warheads of which 2,500 are strategically operational if for some bizarre reason China was in a position to take half of Siberia by force, which it is not.