No empire can stand forever.
Excuse the brief history lesson, but even the great Romans fell. Alexander the Great's empire expanding across almost the entire Eastern World fell. Even the Aztecs, Mayans, Greeks, and Persians all fell.
Sooner or later, all great empires fall—and college football is no different.
Some of the greatest programs in college football have now fallen; it is just part of the vicious cycle that allows teams like Oregon, Stanford, and Oklahoma State to thrive.
But I doubt any thought that these five historically dominant programs would fall into holes this deep.