I have no idea how this war ends, let alone what the world looks like 3-5 years after it does. But I do think nukes aren't in the picture outside of the possibility that foreign armies were to somehow roll into Moscow before surrender and plant the EU flag in the Red Square, a fantasy that isn't worth entertaining.
There are two main examples from history I can think of: balkanization as per Yugoslavia in the early 90s and complete decimation as per Germany in the 40s. You might say that Russia has already had its 40s Germany moment at the end of the Cold War, when Russia went into a modern dark age. The blame for this fell somewhere between the communists of the USSR and the West that the communists were long-staring at. Nevertheless when Russia was rebuilt in 1991 it was rebuilt in the West's image - as a capitalist oligarchy, except it held the same post-Cold War grudges. Germany, the last bastion of the iron curtain, extended an olive branch to Russia and tried tying up the Russian economy in the global economy so much that the economies would be so entwined that if Russia were to pull any string out of line it would hurt itself as much as, and hopefully more, than it would hurt the other economies in the neo-liberal ball of twine.
So for balkanization to happen, there needs to be an anti-regime tinderbox sentiment in Russia that could spark a civil war. And for capitulation the West needs to be as literally independent from Russia's economy as Russia believes its economy figuratively is from the West's.
Whatever happens there'll probably be a treaty of some kind written up in a few years with Ukraine and Russia both signatories, and the current boiling pot simmers back to the uneasy heat of 2014.
www.reuters.com
www.theguardian.com
