There's just a small problem i see:
Putin grew powerful in the shadow of the fall of the Sovjet Union. He, among many others in his back, experienced the fade of the SU as unjustified and cruel, and now it's perfectly reasonable that he (believes) is fighting for a good thing, the reestablishment of the good, old Union. Golden times will come again (and so on)...

Now imagine Russia under Putin ending as an imperial force, all the people under sanctions and poverty, without future visions, a whole nation in misery, just like North Korea, but on a higher scale. A nation's young generation, growing up under grief, with no future, because of the "bad western nazi imperium".
These times might create much more dangerous dictators than Putin.
And don't let us forget about China! Can Europe afford to lose Russia, as the "whore of Bejing"? I don't think so.

Imho, if Putin's regime finally fallls, Europe and the EU should embrace Russia as a part of europe, tear down ideological walls, bring more evenly distributed wealth to the country. As unrealistic as it might seem, it's the only long term solution to the Eurasian conflict. Of course, the EU has to adress their problems with corruption and become a way more serious government than they tried to put up so far. Otherwise the EU will start to crumble. That's why i think Russia should not be isolated after Putins regime ends. Otherwise when will they recover and start another war? 2030-2040?