But this kind of thing does push Russia towards the end goal of dismantling Ukraine as a sovereign state rather than simply taking the Donbas Republics and drawing the line there.

The original Russian policy (under Putin, no less) was to do the same kind of neoliberal puppeteering that Western states accomplished in Germany and Egypt and Japan. Use tight economic relations with the threat of targeted sanctions (and the occasional FSB knee-capper) to keep Ukrainian aristocracy in line. And the western response was to keep fanning the flames of insurrection until the country balkinized like a dropped egg.

Now he's pivoted back to a more traditional boots-on-the-ground occupation, a la America's domination of Haiti and Panama or the USSR dominion over Hungary and Czechoslovakia. And the western response has been to put up a losing counter-insurgency a la South Vietnam.

But the idea of Ukraine as a sovereign state was never really on the table. Ukranians had a shot at picking their own master back in the '00s/'10s. And they might have found a Turkey/Saudi/Israeli style middle-ground, where they played Russia and America off one another for a better position at the Cheap Imports / Military subsidies negotiating table. But they were always doomed to be beholden to someone.

As long as a sovereign Ukraine exists, it will be a hotbed for this kind of pseudo terrorist attack.

Ukranians had no chill. They simply couldn't resist doing their own little Serbian genocide in the East. And as Russia proved in Chechnya, that was a red line they weren't going to let Ukrainian fascists cross. Losing influence over the executive branch for a few years was a pill Putin could swallow (so long as Ukraine didn't mind giving up Crimea). But ethnic cleansing as a tool of political consolidation? Nah, dawg. Not on United Russia's watch.