He clearly doesn’t care about UN laws. He broke UN law invading anyways, then countless war crimes committed by his forces.
It boils down to how many allies he will lose and for how long. And even then it’s only really China that matters and How long would they turn their back on cheap Gas / oil. Is predict they would be back to Russia pretty sharpish after dust settles.
The theory he gets topped before that point is valid but it’s unclear just how strong his hold is as we have been hearing the same for a while.
To put it bluntly, use of a nuclear warhead, be it testing, in international, or own waters, against trees or people will change the face of the conflict in way which to be quite honest neither politicians, media or the rest of the world could comprehend or in fact know.
The only countries flying along with such narrative would be Iran and NK. That's it.
From the moment he drops that war-head, not only will the entire economic system collapse regarding Russia, the whole world's military complex will have a singular focus. Until now, they've been ( UKR ) doing fantastic with the stuff we've been sending. But it's the easy stuff, the beginner and amateur stuff. Let's use this exercise of imagination.
Not only the Whole NATO block, add non NATO allies, Japan, for example, the EU, etc. Now picture all military complex and industry all fixated on a single focal point. This includes, Air Force, Navy, ground Forces, Intelligence Agencies, Satellite, Submarines, anything you want, and the examples can continue. This won't be a contest, or a war. This will be a gruesome, quick, awful execution of all that moves and shoots, and is made of metal and flesh on a massive radius, all at once. There is no insane individual that will choose to go down that route without the immediate death-warrant guaranteed.
The little nonce will be fucked if he does, fuck if he doesn't. As the rest of his decrepit, awful nation.