Under international law mercenaries can be lined up against a wall and shot. Ukraine has chosen to afford them POW status.

On a bigger picture, what you are seeing at the border are the same Cold War games we enjoyed after World War Two. We never shot down a Tupolev after intruding into US territorial waters in Alaska. They were escorted out. It’s the same exact dynamic.

Now, those choppers land troops, one was a troop transport. Or they start shooting, that is another story