Why let them walk away? I can't imagine it happening either, but if it happens, they are enemy combatants. EU should arrest them and treat them as prisoners of war.
You must have forgotten the world has rules and weight classes. But reality hits hard and doesn't care. The USA with this administration is not to be tested. If there is anything you can say about trump. The world is actually terrified at what he will do because he will do anything he thinks is right. Not what is. But he's controlling the strongest most intelligent military on the planet. If you think war or capturing prisoners as another country is safe. You're dumber than the ring leader himself.