Frank Reich, 2023
Of the coaches on this list, this is probably the most comparable situation to what Brian Callahan is dealing with in the present day,. It's honestly still surprising that Reich;s tenure in Carolina flamed out like it did. For one thing, both are offensive minded guys, and with the experience Reich had, you would have figured he would at least do a functional job with Bryce Young's development.
It was a total disaster. The Panthers kicked off their 2023 season with a whimper and were never able to show progress before Reich got fired after Week 12. The play calling was absolutely terrible, and especially after how 2024 ended, it showed that Reich and his staff got nowhere near what they should have out of Young and that offense.
Callahan dealt with a lot of similar things in 2024, such as questionable play calling and the inability to get the Titans to show any true progress. At least in his defense, he had the excuses of being a first-time play caller and having nothing resembling a first overall pick at quarterback.
There were other differences too, such as Reich being a more "past his prime" type of coach than Callahan currently is. Reich did mention after the fact that his tenure with the Panthers was likely the last of his NFL career, so it does make sense to question just how with it he was in Carolina.
Regardless, this situation is the one on this list where it makes sense to think that a similar fate could happen with Callahan.