The legitimate/legal way for Crimea to leave Ukraine is to secede from Ukraine and declare its independence. Hold a vote (a legitimate one recognized by the World)=, not some farce the world is laughing at like the "elections" in Russia). That STILL doesn't give Crimea to Russia. It recognizes it as a sovereign nation, IF it is recognized as one.
THEN Crimea can choose to do business with whoever it wants.
Otherwise, legally, the Crimea is an illegally occupied portion of Ukraine by Russia. End of story. Go argue with the UN or the hundreds of countries that view it just that way from a legal standpoint. You're wasting your time pounding a soapbox here. We don't decide at Debate Policy who Crimea belongs to and you should thank God we don't or you;d STILL be shit out of luck.
“When bad men combine, the good must associate; else they will fall, one by one, an unpitied sacrifice in a contemptible struggle.” Edumnd Burke