When one country walks in military into another sovereign country it’s called an invasion. Russia has no right to invade another country.
Russia’s military is technically there with Ukrainian permission.
But its a lesson to Kiev on who really holds the whip hand. It would be suicidal for Ukraine to go to war against Russia over a prestige prize.
Look for a replay of Transdniester here over 20 years ago. Russian peace-keeping troops move in and they stay there for good.
Better a good frozen conflict than a bad civil war.
Besides, saner heads in Kiev know full well keeping Crimea is not worth the risk of losing the real prize of becoming part of the West. Let it be Moscow’s headache.