Majority of Europe-Asia (southwest, south, southeast) flights route via Turkey/Iraq/Gulf or Romainia/Black Sea/Georgia/Turkmenistan -- especially since MH17.

Those heading to East Asia tend to fly over northern Russia, well away from Ukraine

Here[0] are planes avoiding Ukraine

[0] http://imgur.com/EbNXLpXl.png

Ukraine is a small country, easy to avoid. The GP was talking about Russia in general though, which is much harder to avoid. The traffic to East Asia is far greater and more important than that to Southeast.

The last time a plane was shot down over Russian airspace was KE007 in 1983

International flight paths over Russia are a large source of money for the country, Russia isn't going to shoot down any airlines.

The fact that russian army shot down MH17 from occupied territory doesn't change much really.

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.