Given the rising tide of Orthodox Islam in Turkey I agree that it highly likely that barring outside influence (invasion maybe) Erdogon will be followed by a more Orthodox Muslim than he.
He's shown an aptitude for ruling by fear; that doesn't bode well for either a return to a democratic, pluralistic society with unique safeguards against the rise of Islamofascist regimes, or to the rise of something more like the mullahcracy in Iran. I'd love to be wrong and see him succeeded by secular-minded (which he is at base, but he uses Islam as a political crutch) freely elected officials. Problem is, he's ruling based on a clear majority of the country, a populist if you will. And Turkey serves as the cork in the bottle, a barrier between the real Islamic nutjobs of the Middle East, and Europe.