

That would depend on the details of the hypothetical. Certainly if Ukraine was able to develop a credible threat with first strike survivability before Russia became aware I would expect Russia to be forced to move towards de-escalation and diplomacy because their major cities like Moscow and St. Petersburg which Putin has tried to shield completely from all effects of the war would be in danger.
Lacking that and with a credible ability to eliminate the nuclear weapon completely with a pre-emptive strike Russia would probably do it even if it meant nuclear strikes against Ukraine.












Sadly it has a pretty good chance of affecting many people who never supported him as well.