I think they hope to retain Kerry but may not be able to.They will probably offer him co-dc and a pay cut to 900k ish. He will then have to decide if he wants to pursue other interests or if he wants on the Larry Johnson plan, where he recruits anyone he wants, puts out first round draft picks, and is considered the best position coach at his position. 
 

Kerry probably believes that he could do better at his next shot calling a defense, and he is correct. He was dealt a crappy hand with COVID and very few on the d having game experience this year. They ran a simple scheme at the start of the year because they knew the freshmen and sophomores were players and they rotated to show that. The upperclassmen couldn’t keep the underclassmen off the field because they kept making mistakes as well. 
 

As an aside, A great way to lose the entire locker room is to start half a dozen freshmen who have been there a few weeks over people who have been there three years. The coaches have to eat into the time of the established player to show they have given them a fair shot. Then you lose a few guys to the portal rather than having a split in the team. When you roll that many people in and out you have to simplify. a simplified scheme is enough if the upper classes were more talented, game ready, and better communicators on the field

Barnes is benefiting from players getting better and from a more diverse scheme. Coombs would have benefited from the former, and possibly the latter as well. All that said, Kerry probably isn’t OSU level as a DC, but there were some mitigating factors. 
He was a spectacular HS head coach, again similar to LJ. 
 

IMO he has two options, 1. the LJ plan which includes Co-dc but no play calls or 2. a smaller school as a dc/head coach. He is 60 so starting over might not seem attractive, but he’s only 60 so there is time if he wants it. 
 

If I had to bet money, I’d bet he stays, but the best position for him is as the Head coach.