Russia has genuine strategic interests in Crimea, mainly the naval base which gives it access to southern oceans. Otherwise, its ports are on the Baltic sea or Northern Pacific, a long way from the Mediterranean and Syria, for example. Meanwhile, the US and Western Europe are mainly interested in the abstract principle of preventing the change in national boundaries by military force. That is an admirable principle, but the US has dishonored it by acquiescing for decades in Israel's annexation of territory conquered by its military. For Jewish money, the US has been glad to disregard international law as it applies to Israel. Will it do the same for Russian money? Politico says, "Yes," in one of the most cynical, damning articles that I have read about the loss in integrity in the west, "Why Russia No Longer Fears the West." It says that Western Europe is so greedy to get money from the Russian oligarchs that it will not challenge Putin. Although the article cites the Magnitsky Act as evidence of greater courageousness in the US, it's not much. American banks are just as anxious to get Russian billions as European banks, despite the Dodd-Frank bill, which would put a few more restrictions on American banks, if it ever comes into full force.
My guess is that Ukraine will end up being partitioned in some way, preserving Russian influence at least in Crimea, if not in all of Ukraine. Putin would prefer to keep all of Ukraine in the Russian orbit, but may be willing to compromise to avoid a wider war or draconian sanctions on Russia. I would guess that he wants Kiev more than western Ukraine, since it was the ancestral capital of Russia, predating Moscow. The Polish Ukrainian border has moved east and west over the centuries, and part of what is now Ukraine used to be part of Poland and part of the Austro-Hungarian empire, but a Ukraine that did not include Kiev would not be much of a country. So, I would guess that Putin's first choice will be to keep all of Ukraine in the Soviet sphere of influence. Perhaps the West can negotiate some sort of compromise, but when Yugoslavia disintegrated, the West facilitated its partition along ethnic lines.