Three possible outcomes;

1) Russia-Ukraine agree to some sort of truce. Since Russia has a "hard on" for Ukraine, it becomes like our Iraq 1 and Iraq 2, the prelude to a future conflict with a smarter Russia (except by this time Ukraine has joined NATO).

2) A long, protracted "Vietnam" that results in regime change in Russia. Russia renews rivalry with China, becomes more friendly to West as means to save its economy.

3) Russia deploys nukes, WW III ensues, Russia in ruins, rebuilt by West.

4) The West gets tired of costly support, Russia stays the course and somehow wins while making the rest of world dependent on their oil etc.

Of course 2 is the best outcome for us, 4 the worse, 1 probably most likely. Western support for 2 avoids a very costly future 1, 3 or 4.