When will they have this choice? Why not put a UN peacekeeping force in Crimea and the four other areas under Russian control until free and fair elections can be held under the auspices of OSCE?
Why do Crimeans need a UN peacekeeping force? They are Russian and have a Russian peacekeeping force. They have voted three times since 1991 to join Russia. Crimeans wanted to stay with Russia when the Soviet Union broke up in 1991. They voted overwhelmingly in a referendum to remain with Russia but Russia was in no position to recognise this.
They have voted twice since then, again overwhelmingly in favour of joining Russia. They neither need nor want outside interference. They are Russian. Why are you so concerned with a people you clearly know nothing about?
All Ukrainians will be given a vote when their country has been demilitarised. It's what happens when you live next door to a nuclear superpower and allow yourself to be used to provoke and antagonise your bigger stronger neighbour. They will be demilitarised and then choose who they are and who they wish to align with.