Russia will annhilate nobody, and there obsolete navy would be dispatched fairly quickly.
The Russian vote was illegal and not relevant to the constitution of the Ukraine.
Ukraine was ceded Crimea by the valid government in Russian/USSR. The sovereign government of Ukraine has never ceded it back. It was stolen, illegally.
European governments do not recognize the illegal annexation to this day.
Do a little research regarding Kosovo precedent.
UN Court concluded that the right of the people to self-determination is supreme to national legislation.