Well, since Ukraine is not a Nato nation, these big troop buildups are really just temporary and no real threat to Putin. At least, that is the way I would see it if I were him.
And if they do actually attack, all bets are off for world peace in general. Get yourself a good bomb shelter - or cyanide pills.
That's the way I would see it too, but what's dangerous about this is that Putin may not, and probably will not, see it that way.