"I believe that man will not merely endure: he will prevail. He is immortal, not because he alone among creatures has an inexhaustible voice, but because he has a soul, a spirit capable of compassion and sacrifice and endurance." William Faulkner
Anyway. If that is what they do, escalate and make a demonstration that scares the world. Be very open about it ans explain that it is plain deterrent. Unless we get the UN to guarantee international security robustly, we will have to resort to that type of thing within about 10 years anyway. So why not save ourselves the cash and do it now? The advantage would be that like after Iraq2 the membership of the UN would be more willing to do things they are otherwise reluctant to commit to, as the 2005 r2p norm change showed.
Killing one person is murder, killing 100,000 is foreign policy
If the country retaliated in some way, the SC again is no longer of any help. And as it does not guarantee the security of the members and especially populations, it is more a danger to world peace than the help it was in the post 1950 era. Nobody is saying this out loud yet, but that was the reason for the 2005 shift in focus, which has faded somewhat now. And if we cannot get the UN filling the policing job, there will be major war in any event within thirty five or so years. That is almost inescapable and diplomacy cannot prevent it indefinitely, though, there are some dinosaurs that think it possible.