Tearing down the wall cost Gorbachev politically, but the wall is gone and freedom won.
Gorbachev faced problems in the Warsaw Pact that made the non-Russian countries therein uncontrollable. The “’stans” hadn’t been listening to Moscow for 15 years. Germany and Germans wanted the wall down, not Moscow, and Gorby did not have the horsepower to stop them.
Putin faces no such problems. In fact the rise of Russian nationalism is what led him to conduct the Crimean Invasion to deflect unrest over internal economic political problems within Mother Russia.
Russia has no intent, or even political capability to “give back” Crimea. The US and Ukraine do not have the political nor military capability to make them do so, and if we had such political capital, it would be much better spent elsewhere.
For example, to work together to force the PRC to put their North Korean dog back on its leash.
Finally, the local citizenry of Crimea are generally very happy that Russia took over. Granted many are not, but there is no groundswell of public opinion there to return to the orbit of a (nonexistent) Mother Ukraine.