Putin does not want to negotiate about Crimea. He does not talk with the current Ukrainian government. He repeats his version of events to those he talks to. He is still lying about Russian troops not taking part in the events in the Crimea. It's a blatant lie. I wonder what Russians think about it. They must know it too.
Crimea is controlled by Russia. That's a fact. Crimea will become part of Russia officially in a few days. The remaining troops loyal to Ukraine will be treated as foreign forces, and will be attacked.
What should Ukraine do? If I was the Ukrainian government, to protect life, and the remaining parts of the Ukraine, I would ask the loyal Ukrainian troops in Crimea to surrender weapons. I would seal the borders with Russia and Crimea. I would delegalise far-right parties in Ukraine. I would have referendums in eastern parts of Ukraine - if they want to join Russia too, let them go. Ukraine, and the people living in its borders currently will be stronger, better off, and most importantly alive, if they go their own ways. There is no point in starting a war for a line on a map. Putin will not live forever and Russia may have a democratic government in the future. Until then we live and wait.