If re-unification of the Soviet empire is Putin’s desire… then Estonia, Latvia and Lithuania must also be getting worried? They broke off over a hundred years ago… but it would shore up his European border to reclaim them.
And given the response so far from the West, assuming these sanctions have little/insufficient effect… (And, one has to assume he would have expected sanctions being imposed) You have to expect him to feel pretty invincible right now.
I’m thinking the best hope here is if Ukraine are able to continue to resist long enough to see a high number of Russian deaths - maybe Putin will face enough internal backlash to halt him? I see 1,400 protestors were already arrested… that’s 1,400 very brave people to protest against Putin in Russia!