I hope no more people die for political reasons in Ukraine. I hope the Ukrainian government stands the ground and does not let itself get provoked. Putin's Russia is the aggressor here in political terms. His armed men are taking control of Crimea, which is politically part of Ukraine.
What should Ukraine do? Talk. Negotiate. Get the European Union, China, and the U.S. to convince Putin to talk. Make it clear for Putin that it is cheaper for Russia to negotiate a deal than to suffer sanctions.
There are Tatars, Ukrainians and Russians in Crimea. If Crimea is to become part of Russia, then Tatars living there should be given a chance to create their own country in Crimea or should be compensated to move to Ukraine. Ukrainians living in Crimea should be given similar choice. Russia has money. Let it buy Crimea. Life of innocent people is most important.
Of course, negotiating with Putin may not work. He's just breaking an agreement he made with Ukraine when it gave up its nuclear weapons. As long as Russians support Putin and the vision of an empire, there may not be much to do.