> although the next leader may not be any less of a threat.

This is very important to remember

In the event that the current Russian government falls and sees some sort of return to democracy, freedom, and respect for neighbors, there will be a desire among some in the west to embrace this, to trust Russia, to expand trade with them and be friendly. But this already happened before and then Russia went back to the bad old days. And it can happen again. If Russia sees a change in leadership and a turn inward, the west mustn't get overly trusting - instead it should keep decoupling from the Russian economy, expanding NATO up to Russian borders as much as possible, and investing not in rebuilding Russia but in boosting the neighbors bordering Russia. If Russia still tolerates it, then a slow cautious thaw in relations can occur, and if Russia seethes with rage and quickly goes back to the bad old days again in response, well, the west will be more ready and more of Russia's neighbors will be defended by the NATO nuclear MADman umbrella