Of course, all of this unpleasentness could have been avoided if, after independence in 1991, Ukraine had taken a leaf out of Russia's book and how that country dealt with the populations of Konigsberg and the Kuril Islands.
Rather than pander to the rights of minorities, as Ukraine has had to do in Crimea, just expel them all and repopulate with your own kind. No need then to worry about future generations wanting to reunify with their former homelands.