Andrew, these hypothetical situations to me underplay the role of nuclear fallout - I confess I don't know how bad that will be, but anyone who wants to conquer territory does not want to nuke it first--they will will an wasteland. And, fallout travels across borders. A strike in Ukraine, so it seems to me, would likely hurt Belarus or Russia proper, depending on which way the wind is blowing. I would love to get some detailed analysis on this, to better understand the probabilities, as Russia must be calculating it.

Also, you have not addressed Russia's nuclear main of command. Who stands between Putin and a nuclear launch? Would ordering an attack amount to ordering a coup?

These unanswered questions prevent me from taking your dire analysis at face value.