Based on this article (from 2017) the buyout right now is about a wash compared to what football makes the university annually. Or, put plainly- the buyout isn't an issue when football revenue starts to fall because you almost can't afford to keep paying him.
Also- this is from the mediocre 2016 season. I'll wager that 2013, 2010, 2004, maybe even 2018 had higher revenue.
"Football is a $23.5 million per year business for Auburn University, according to data collected from USA Today and the U.S. Department of Education and published in 2016 by Business Insider."