I'm guessing Saban's replacement will be Mike Tomlin. By Sherlock Holmes logic, i.e., after you're eliminated all the other possibilities, what remains, no matter how unlikely it seems, is the answer to the puzzle.
Never had a losing season. One of the very few coaches who you would not expect to experience/allow a post-Saban recession.
When he says "We'll do pro concepts, and can develop you for the NFL," 5-star high school kids will believe him. If he maintains the Saban infrastructure of support analysts, recruiting will not fall off.
Obviously the challenge would be getting him to leave the NFL to try something a bit different. The opportunity to be acknowledged as the greatest black college football coach of all time, based on national championships won, could be that lever. He's only 49 years old.