Spencer Hall posted a beautifully written piece on what might bring the end to the current Alabama dynasty, comparing it to Nebraska in the '90s and looking at where the threats to it lie now. I disagree some with the approach and with the conclusions.
Figuring out why Nebraska fell off is a fairly easy thing to: Tom Osborne retired. Frank Solich kept it going at a reduced level for a while, reaching another brief peak with Eric Crouch, but Solich was no Osborne. Steve Pedersen fired Solich and hired Bill Callahan, and the rest is history. If Bama falls off when Saban retires, the decline won't be shrouded in mystery.
To see how dynasties can fall off without the head coach leaving, I'd have looked more towards USC under Pete Carroll. It was a monster of a program, winning all or a share of two national titles and requiring a heroic effort from Vince Young to deny it of a third. And then all of a sudden, it just wasn't the best anymore. The decline did begin somewhere around when OC Norm Chow left, but given what he's done after leaving USC, I'm less inclined than I used to be to point to that and call it a day.
After all, the teams were still quite good. The 2008 defense in particular was one of the absolute best of the decade. Carroll just lost the ability to win on the road with the same consistency as at home. Of USC's five losses across 2006-08, four came away from the Coliseum. The one home loss was the famous upset by a really bad Stanford team in '07, which came a year after USC's epic last-weekend flop against eventual 7-6 UCLA. I'll let you decide whether losing to nine-win Oregon State teams in both 2006 and 2008 also counts as "losing to a team you have no business losing to", but those indiscretions indicate the program that lacked focus at bad times. Eventually, it seems that expecting to win solely because you showed up happens to every great regime. I think that could have hurt Alabama some in 2010, to bring it back to Saban briefly.
The line between undefeated and one or two losses can be razor thin, and that was the case for those Trojans. Guys just didn't quite pan out like they used to. Joe McKnight was supposed to be the next Reggie Bush, but he wasn't. John David Booty and Mark Sanchez were not Matt Leinart and Carson Palmer. Taylor Mays was a fearsome hitter from the safety spot, but his coverage was lacking compared to his predecessors. A few of these things happening at once can be overcome, but if they all happen at the same time, a program can't help but fall off from being elite every year.
In 2009, when Carroll went with freshman Matt Barkley because he didn't have a single other reliable quarterback, the decline really set in. Carroll then skipped town right as the NCAA sanctions were about to hit. Lane Kiffin has done a better job than I thought he would getting things back up, but as much as anything, it's because guys like Barkley, Robert Woods, and Marquise Lee are panning out (or being well developed by the coaches) again.
Look at another dynasty that fell off even more dramatically: Florida under Urban Meyer. The Gators won 13 games in three out of four seasons, and then suddenly the program could barely do a thing well. Dan Mullen leaving for Starkville and Meyer's coming and going didn't help, but it didn't look like the same team in the least in 2010.
John Brantley was never going to be a perfect fit in Meyer's offense, but he played like a two-star quarterback instead of the four-star quarterback he was billed as. Andre Debose was supposed to be the next Percy Harvin, but he wasn't. All the receivers, for that matter, looked no better than David Nelson, who was the fourth option on the '09 team. There was no explosive pass rusher to replace Carlos Dunlap, and the team hadn't had a great DT rotation since 2006 anyway.
Florida didn't drop off in the recruiting rankings, just as USC never did either. The coaches either lost their eye for talent or their ability to develop it. Some of that easily could simply be the law of averages setting in: you're not going to hit on every four- or five-star player you sign for too many years in a row. Some percentage of blue chip recruits are going to be busts, and just as some years most of them work out, some years most don't.
If I'm correct in my diagnosis of USC's and Florida's falls—that the root cause is players not panning out or being developed well—then Alabama fans have little to worry about for now. That's because Saban does something that Carroll and Meyer did not: he oversigns. He can better deal with a bad year where too many highly rated guys bust because he simply brings in a lot more players. Even with the new SEC rule with the 25-players-per-year cap, by my count he's still comfortably over the 85-scholarship limit right now.
Having a consistently good roster is, after all, the whole reason why coaches who oversign do it. Forget all the politics surrounding the practice for a moment and look at the plain effect. Your best 50-60 players who play the majority of the snaps are going to be better if you have a larger pool of talent to choose from, provided you bring in highly rated classes every year. Saban certainly has been bringing in highly rated classes, so he's going to have a competitive advantage from oversiging.
I don't see USC or Dana Holgorsen at West Virginia as the primary threats to Alabama's run of success as Spencer does. USC is going to fall off due to its enormous sanctions here soon, and West Virginia simply cannot compete with a fully focused Saban at a place like Alabama.
If Alabama is going to decline with Saban still there, I see only three avenues of getting there. One is if somehow a couple of other SEC coaches somehow leapfrog Saban schematically. Given how good Saban is, that doesn't seem likely to me. The next is the natural slowing down that comes with aging, but we're still a few years off from that setting in. The third would be national adoption of Big Ten-style oversigning rules that limit programs' ability to go over the 85-scholarship cap. I don't know how imminent that would be (not very, I'm guessing), but it would make Saban more vulnerable to falling off thanks to having a couple of bad and/or small classes in a row.
Maybe Alabama will take some steps back in the pecking order in the West if Les Miles keeps it up, Scot Loeffler turns out to be a genius at Auburn, and Texas A&M parlays its new SEC membership into recruiting dominance in its home state. Kevin Sumlin does run a Holgorsen-style Airraid, after all, which would directly threaten Saban in the ways Spencer described WVU possibly causing him some issues. I hesitate to point to new schemes as world changers though; Nebraska's option was already a relic in the '90s when Osborne trashed the rest of the country with it. With the right kind of great players, anyone can win with any system in college football.
All of us non-Alabama fans are stuck with Saban dominating for a while unless any of those three things I mentioned before set in sooner than expected. Saban going to Alabama is one of those rare right-place-right-time fits where a coach comes in and wakes a sleeping giant. They only happen about two or three times a decade. We saw that with Steve Spurrier at Florida in 1990, Bob Stoops at Oklahoma in 1999, arguably Jim Tressel at Ohio State in 2001 (depending on how down you think OSU was under John Cooper), Carroll at USC in 2001, and Saban at Alabama in 2007. Meyer at Ohio State might be the first of this new decade, provided he can keep his stress level down.
With Alabama at such a high level and with his coaching tree sprouting new branches every year, the end of Sabanball is not near either in Tuscaloosa or nationwide.