I did some data analysis around this, and here's what I found:
There have been 40 coaches who have coached for 15+ years at the same school while having at least one season coached in the last 40 years (i.e. were still coaching in 1984). For these coaches, I set a beginning limit of 1973 when the first scholarship limits were put in place. Five coaches are still active in the only CFB HC job they've had - Kirk Ferentz (Iowa), Mike Gundy (Ok St.), Kyle Whittingham (Utah), Troy Calhoun (Air Force) and Dabo Swinney (Clemson). For 31 of the other 35 coaches, it was either their only head coaching job in CFB or their last one. Rich Brooks (Oregon, first job, went to NFL), Mark Richt (Georgia, first job, went to Miami after being fired), Mack Brown (Texas, UNC before and after) and Johnny Majors (Tennessee, went to Pitt after) were the four who didn't fit the criteria.
I used Sports Reference's simple rating system (SRS) to look at each coach's seasons, and highlighted their top and bottom seasons (3 for 15-19 years, 4 for 20-24 years, 5 for 25+). I also did not include the 2020 COVID season for those coaches who were active given the uniqueness of that year.
Looking at coaches who had back to back seasons that were in their bottom 3/4/5 years after they had already coached 10+ seasons:
Joe Paterno (PSU) - 2000-01 (10-13, 8-8), 2003-04 (7-16, 3-13). Somehow managed to survive both of these runs and coach for another 7 years until, well, you know.
Bobby Bowden (FSU) - 2006-07 (14-12, 7-9). These seasons were the beginning of the end, as he was fired after the 2009 season.
Tom Osborne (NEB) - 1988-91 (39-9-1, 24-3-1). A bit of a caveat needed here, as these were not bad seasons by any stretch, given that they made two Orange Bowls and won two conference titles. They were four of his worst five seasons though.
Fisher DeBerry (Air Force) - 2005-06 (8-15, 6-10). Retired following the 2006 season after 23 years.
Grant Teaff (Baylor) - 1987-88 (12-10, 5-9). Had some leeway after winning bowls in 1985-86, but this was the beginning of the end for him. He coached four more years, finishing with a bowl win in his final game before resigning to become the AD.
Terry Donahue (UCLA) - 1989-90 (8-13-1, 6-9-1). Another coach who had leeway from winning 7 bowl games in a row and being ranked as high as #1 in 1988. Coached five more seasons, including making the '93 Rose Bowl after starting the year unranked, before resigning to go into broadcasting.
Hayden Fry (Iowa) - 1992-93 (11-13, 7-9). Rebounded with Sun Bowl and Alamo Bowl wins in 1995-96, but retired after the worst season of his career in 1998.
Barry Switzer (OK) - 1983-84 (17-6-1, 11-3). Much like Tom Osborne, these were not bad seasons per se. Switzer declined a lesser bowl bid in 1983 and made it to the Orange Bowl in 1984 before winning the national championship in 1985. He resigned following the 1988 season under scandal due to players getting paid and one player attempting to sell coke to an FBI agent...
Sonny Lubick (CSU) - 2005-07 (13-23, 8-16). Lubick was fired after the 2007 season and opened a steakhouse in Fort Collins.
Fitz (NU) - 2021-22 (4-20, 2-16).
So only DeBerry and Lubick left their jobs immediately following back to back bottom seasons, though the record for both was better than Fitz's.
Also looked at 5-year averages, which showed me that 24 of the 35 coaches on this list left their jobs following a real slide in the quality of their programs compared to past performance. The only coaches who did not leave due to the declining quality of their teams were:
Tom Osborne - Retired after 25 seasons following three national championships in four years (1994, 95, 97)
George Welsh (UVA) - Retired after 19 seasons due to health issues. Took Virginia out of their 30-year-long dark ages, won 2 ACC championships, was ranked #1 in 1990 briefly, and handed FSU their first ACC loss after 29 straight wins since joining the conference. Retired as the winningest coach in ACC history before being passed by Bowden.
Don James (Washington) - Resigned just prior to the 1993 season under controversy following back-to-back-to-back Rose Bowls due to allegations of paying players and a lack of institutional control on recruiting visits.
Rich Brooks - Left Oregon following their first Rose Bowl appearance since 1957 to become the head coach of the St. Louis Rams in 1995. Lasted two years before being fired.
Rick Stockstill (MTSU) - Despite winning bowl games in 2021-22, he was fired after 18 seasons last year.
Bo Schembechler (Michigan) - Retired after the 1989 season due to health concerns following 3 Rose Bowl appearances in 4 seasons (1986, 88, 89).
Barry Switzer - See above.
Johnny Majors - Forced to resign following heart surgery after 16 seasons. Speculated that his assistant and interim head coach, Phil Fulmer, engaged in backroom shenanigans to force Majors out.
Barry Alvarez (UW) - Retired following a Capital One bowl game win in 2005 after 16 seasons to become the AD.
Frank Solich (Ohio) - Retired due to health reasons in 2021 after 16 seasons, having taken Ohio to bowl games in 10 of 11 seasons, winning their last 3.
Gary Pinkel (Mizzou) - Retired due to cancer in 2015 after 15 seasons, including back-to-back SEC division titles in 2013-14 including wins in the Cotton and Citrus bowls.
The other coaches who made this list but didn't meet any of the previous criteria: Frank Beamer (VT), Lavell Edwards (BYU), Gary Patterson (TCU), Don Nehlen (WVU), Bob Stoops (OK), Nick Saban (Bama), Phil Fulmer (Tennessee), Bill Snyder (KSU), Jeff Bower (S. Miss.), Jim Sweeney and Pat Hill (Fresno St.), Vince Dooley (UGA), Ken Niumatalolo (Navy), and Herb Deromedi (C. Michigan).
I hope you enjoyed wasting your time reading this as much as I did in researching this.
