Russia's only southern warm water naval base is in Sevastopol. There is no possible way that Putin would lose that to the potential that Ukraine joins NATO.
I also am not worked up over Crimea because I look at that as a military and political reality. Plus some of the Russian-controlled history as you've mentioned... Even though Crimea has changed hands throughout history, multiple times (originally the Greeks, who founded the coastal villages at the time, Turkey, Ukraine, Russia, Crimean Tatars, etc...), and, therefore do not recognize Russian sovereignty based on "history".... I fallback on the military reality of Crimea: No. Possible. Way. Putin. Will Lose. Crimea.
On the other hand, I have contempt for him running Russian troops into parts of Georgia, Moldova, and Ukraine (the Donbass) simply because he wants to screw with his neighboring countries.