Yanukovych wasn't strung up by protestors, he was removed from power by a huge majority of the Ukrainian parliament, including members of Yanukovych's own party, and they held an election later that year. For what you're saying to make sense, any large protest in a country would have to potentially void any international treaty that country is party to. Russia doesn't get to invade and annex land just because there was a big protest and then the parliament kicked the president out.