Assuming that it was even legitimate to begin with

"Democracy is when the stupid foreigners vote how I think they should, otherwise it's not legitimate"

doesn't automatically legitimize relinquishing territory to a foreign nation.

If the people vote overwhelmingly to leave Ukraine, then that shows that Crimea isn't Ukraine's to relinquish or not. Liberals and abandoning democracy as soon as it becomes a rhetorical inconvenience for them, name a more iconic duo.