You're right, it would not cease to be useful. But it would cease to be dominant because less people would find it accessible. Search engines allow the average user to orient themselves in the world wide web. It is a large part of why people leave the ordered safety of other mediums for the web. Without organization data is meaningless. And while you and I may be adept at navigating the web without the Google and Yahoos most people would be utterly lost and drown in a vast sea of information.