As long as it geographically remains within Ukraine's borders, the ownership would not matter that much (assuming that the Ukrainians are not dumb enough to sell it to the Russian interests). As for the closing it down - this option would cause significant social friction due to rising unemployment. Keeping it open and supplying the proposed coal conversion plants could:
1° provide a strategic resource [oil];
2° keep a lot of people employed [large social stability benefit] and
3° free the Ukrainian state from [large part of] its economic dependence on Russia [geostrategic benefit].
Speak of killing THREE birds with one stone...
this option would cause significant social friction due to rising unemployment. The EU in a word: Germany 12.5% and rising, France 11% and rising, Poland (was down to 18% before EU membership, now 19.5%). No, the coal industry is being nationalized and will become another bureaucracy, run with all the efficiency that the Soviets ran it with: ZERO.