I guess that's always a possibility. Another more likely scenario in the next few decades is that Russia and/or China will collapse into violent revolution or

I guess that's always a possibility. Another more likely scenario in the next few decades is that Russia and/or China will collapse into violent revolution or civil way — as has happened multiple times throughout their long histories. Vladimir Putin and Xi Jinping aren't immortal. They have effectively concentrated decision making in their own hands and purged all other internal power centers, leaving no clear succession plan. When they die there's no way to predict what might happen.