Huh? Why is that the only option? It was part of Ukraine before the Russian invasion. It can be part of Ukraine again.
That would mean, in turn, that ISIS has a new base, right on the edge of Europe.
I think you don't know what ISIS is if you think that Turkey and ISIS are indistinguishable.
It is noticeable that ISIS always comes down from the north - into Syria and Iraq. Where, then are their supply lines?
It was flagrant that when the US tried to set up its face-saving coalition to fight ISIS, that Turkey refused to participate. They have an army with thousands of tanks, but sent precisely none to combat ISIS, right near their own border. The official reason, was because the Kurds were a greater danger.