Unless Russia has some type of “strategic plan” then they just bought a mess. Ukraine provides all of Crimea’s power and freshwater across the Perekop Isthmus. Since there was already a problem with this in Sevastopol BEFORE the Russian invasion, how they plan on alleviating this without paying through the nose to do so, isn’t quite clear.
There’s also the matter of Crimean Tartars. Russia already has a low-intensity terror conflict going in the Trans-Caucasus- How they figure that they can manage two of these, especially since the West isn’t going to be too eager to assist, seems to have been forgotten in all of this. Ethnic cleansing isn’t as easy as it was in times past.
Finally, Russia is a basket case. 2/3s of its foreign currency is coming the sale of natural resources. For a nation of its size and with its complex problems, this isn’t a sustainable economic model. Coupled with its decreasing life expectancy and rampant social ills, taking on another headache in Ukraine seems to be a recipe for a slow collapse of Russia as a whole.
Unless Putin is “declaring victory” now and then quietly withdrawing in the next year or so, he just began what could be another Russian civil conflict. The last one didn’t work out so well for the country.