Bring back? That seems to imply it's not already there.
It's not. There are several nations like Ukraine, (Glorious Nation of) Kazakhstan, Latvia and the other Balkan States, etc. that were all part of the Soviet Union that are independent states (at least nominally, to varying degrees of Putinist oligarchy controlling them). It's part of why Putin wants to invade so many countries.
Na we don't think that... Saturday Morning Cartoon Villains don't win and get to keep the lands they undermine and invade.
Crimea a river. Until the humanity escapes into space the world powers must stay in balance to each other. Weak Russia would bring chaos around it. You don't want some 'stans have accesses to soviet nukes, don't you?
Trust me, in a thousand years no-one would remember that tiny blitzkrieg he pulled once in his lifetime.