I quite agree that we're not looking at something like genocide
here, and your arguments - like those of @Valdore Javorsky
earlier - certainly have merit. I would not discount the possibility that most everyone reacts in a reasonable manner, and that we end up with a Post-Russian Kaliningrad that voluntarily disarms in exchange for substantial EU support (and a road to membership), and which will then be able to receive the Russian refugees from the Arctic territories (as well as those who were abroad during the event, and those who do not wish to live on Sakhalin, which I really
think the Japanese would nab - even if 'just' as a protectorate - considering their historical claims.)
But then, there's the more pessimistic outlook. My own take on humanity is that uncertainty tends to bring humans back to more base urges and instincts. Civilisation is certainty, and that is a shell we have built for ourselves. When there is chaos, when there is vast, supernatural change and complete uncertainty ("Are these the End Times?
"), I think some people will prove to be heroes... and many others will prove to be quite less than that.
Russia is gone. Russia, which just yesterday was - or seemed to be - on the brink of war with NATO. It is gone. Is this providence? Is this the apocalypse? Is this a sign from God? What is happening?! -- Wait, there are still Russians left. Broadcasts from Sakhalin, emergency signals from the Arctic... and Kaliningrad is still there, receiving no word from Moscow. Over there, panic reigns. Has the West annihilated the Motherland with atomics?
Certain military commanders start fiddling nervously with those launch codes they have on them...
In Europe, once the reality of the situation dawns on everyone, it will soon become evident that there is going to be a major problem come winter. Securing "strategic resources" is paramount. Poland and Lithuania will be rather more worried about an imminent threat huddled between them. I can easily see them rolling into Kalingrad, with EU support, offering EU help to rebuild Russia from "the unexplained cataclysm" in exchange for disarmament.
Later on, it will become clear that various other powers are moving into former Russian territory. It would not surprise me if Poland and Lithuania decided on a line of control, and essentially each annexed "their" part of Kalingrad. This does not have to involve killing all Russians, but considering tensions (and potential for worse), both nations may strongly encourage lots of Russians to move to the "Russian Development Zone", where a (much smaller) Russian homeland is being built with extensive NATO and EU support.
I fully expect the EU and NATO to support Finland, Estonia, Latvia, Ukraine and Georgia expanding into former Russian territory (and Belarus, too, if it is smart enough to pivot its allegiance to the West). These countries will likely be offered fast-track entry into the EU and NATO if they behave and cause no problems. "New Russia" will get the same offer, I imagine-- once it's sufficiently rebuilt to even function independently.
Kazakhstan will be ambitious in its claims, probably, which NATO will tolerate as long as Kazakhstan doesn't infringe on the strategic resource-rich regions NATO has prioritised for its own benefit.
In the East, China wll be moving rapidly and ruthlessly, knowing a land-rush when it sees one. Japan will assume conrol over Sakhalin (and the Kurils), partially to keep the Chinese out (thus gaining US backing for it) and partially to get something they've wanted for a long time.
In North-Eastern (ex-)Russia, the USA will likely move in with military force, for keep the Chinese hemmed in and to gain some resources on the cheap.
...and that's pretty much it. That's what I see happening. Without meaning to insult @TheDetailer
by appropriating the scenario for another
edit... I've cooked up another edit. (Truly, take it as a compliment: this whole ISOT has clearly captured a lot of peoples' attention!)
This mock-up below serves to illustrate what I think the final "outcome" would be. (Map adjusted for SUCK, potential geostrategic effects on the wider world ignored.) I think it's fairly self-explanatory, except maybe the blue area-- which is a NATO-administred "strategic resource area", where oil and gas are being pumped up to supply Europe. In time, the Russians may regain authority over the area (provided satisfactory treaties to supply Europe with oil and gas are signed)... but that's a long way off.