Real Clear World links to an article at 19fortyfive.com with this provocative title: "There Is No Military Path for Ukraine to 'Defeat' Russia." I've read it, and that is the conclusion reached by conventional military analysis.
Instapundit links to the same article, and adds this comment which I find more persuasive: "I wouldn’t make too much of this statement. There was no military path for Vietnam to defeat the United States either. Or for the Taliban. And yet."
Gengis Khan got away with genocide. I'd like to think Vladimir Putin can't.
As long as outside arms and ammo keep trickling in, and the indigenes keep wanting independence, the result depends on Russia's appetite for a "forever war." The more powerful and repressive USSR tired of it in Afghanistan. What's your guess?