Taking Crimea had been a ruskie goal since the collapse of the USSR. The ruskie parliament voted unanimously (or close to it) to annex Crimea when Putin seized it in 2014. Recapturing Crimea is a stated goal of Ukraine. How Russia would react to such a loss is a question mark.

Russia could make a formal declaration of war and mobilze, but that would mean an unpopular draft and it would take months to train the new troops. I don’t see Russia going to the nuclear option but it can’t be ruled out. There’s also a strong possibility such a huge defeat could lead to Putin’s removal from power. No assurance whoever replaced him would be better but it would be great to see him gone from the world stage.