History is littered with "never"s that eventually happened. Monarchies, aristocracy, slavery, feudalism, serfdom, empire, mercantilism, all would "never" be replaced ... until they were. Even three centuries ago the idea that we'd be discussing how representative democracies might react to the existence of an anarchistic commune would be an absurd conversation, just not in the way that you might think it is. Not too long ago to be a republican was to be unbelievably radical[0], now it's the majority position for the post-industrial world.

Furthermore, arguably there are plenty of cases of less hierarchical organizations beating out more hierarchical ones. This commonly crops up in military conflicts with decentralized decision making trouncing strict hierarchical militaries, usually in the form of guerilla warfare. I would also argue that the (so far) triumph of representative democracy and capitalism over feudalism and monarchy as a triumph of the less hierarchical over the more hierarchical.

Does that mean that anarchism will come? Heavens no. I would not deign to try and predict such chaotic things as revolutions and forms of government. The transition from monarchy to republic was chaotic and often unplanned, even by the very men and women who mounted the barricades to topple the old forms of government. But I would absolutely not be so confident to say "always" and "never", those statements are far too certain about an unpredictable process.

0 - In the early days of the French Revolution even Robespierre was opposed to toppling the monarchy and replacing it with a republic, and he was never exactly a moderate at any point in his life. The overton window on republicanism has moved a lot in a few centuries.