Correct. That was over Ukraine, and airlines responded by not routing over an active warzone If a plane were shot down over Siberia, planes would reroute away

Correct. That was over Ukraine, and airlines responded by not routing over an active warzone If a plane were shot down over Siberia, planes would reroute away from Siberia, meaning Russia loses overfly money. Unless the scenario is that Russia comes out and says "we'll shoot down non-Russian airlines", in which case Russian airlines are no longer allowed to fly to other countries, and Russia is cut off from the rest of the world, and we go back to routing via Iran or Alaska (perhaps non-stop). It's an extra 1300 miles from London to Tokyo via those routes, 1200 miles to Beijing, 1000 to Shanghai, and only 600 miles to Hong Kong / Chengdu It'd be annoying, but not even as bad as when it was the USSR. Russia meanwhile would collapse economically.