Logan Lee technically has a year of eligibility left, but has said that he is not returning. Chris Reames and Kyler Fisher have a sixth year to use as well, but it doesn't appear that either have been asked to return. That might change if Nick Jackson decides to not take his extra year. We are still waiting on Castro, Schulte, and Jackson to decide (as well as DeJean obviously).
DE looks good with Craig and Hurkett starting, and Brian Allen and Max Llewellyn providing depth. Caden Crawford also got some limited run last year (3 snaps on D). Kenny Merrieweather will be a RS FR but needs to still add strength. It's unlikely that the freshman (Joseph Anderson, Chima Chineke, and Drew Campbell) will be asked to play much of a role on defense.
I'm a bit concerned with the interior DL. Graves and Black provide a potentially elite starting duo, but the depth is limited. Jeremiah Pittman has the third most experience (only 139 snaps) and his play wasn't great. He wasn't relied on to play many snaps as the season progressed. However, he is entering his fourth year and therefore there is hope that everything clicks. Walk on Luke Gaffney actually has the fourth most experience, with a whopping 1 snap on defense. Jeff Bowie hasn't been able to stay healthy. Chase Brackney and Maddux Borcherding-Johnson are still very green and incoming FR Devan Kennedy needs to add a lot of weight and strength before he can be relied on. It is possible that Brian Allen could get some snaps inside, as he is pretty large already and likely not done adding weight. Maybe the staff also moves Griffin Liddle back to DT, but he hasn't been able to stay healthy either and has yet to play a snap either side of the ball.
LB will be set if Jackson comes back. Higgins and Jackson is a crazy good duo. I'm guessing Karson Sharar takes over for Fisher, but Jaden Harrell and Jaxon Reroth will also compete for that spot. There are a lot of ST contributors like Twedt, Montgomery, Telander, and Pollock. Aidan Hall played some limited STs as well. Van Kekerix is on scholly. But I think the future at LB is Kueter, Weisskopf, Buffington, and Reis. Looks like a bright future there.
Assuming Cooper is gone, the CBs will be Harris and Lee, with TJ Hall, Deavin Hilson, and John Nestor providing depth. Teegan Davis has been injured and I believe he was still in a boot during the Big 10 Championship. Who knows when he will be healthy enough to play. Godfrey and Watson will be incoming freshman. If Castro leaves, then I suspect that Nestor might be next in line for CASH. If Schulte comes back then he will start next to X, with Entringer and Kolarik serving as backups. Zach Lutmer might push for a spot on the two-deeps too. Khalil Tate will be entering his second year and could also practice at corner.
If Cooper, Schulte, Castro, and Jackson come back, then we are set. If not, then we should be looking to add another corner and possibly safety in the portal, depending on how the staff feels about Lutmer, Tate, Hilson, Davis, etc. I haven't heard too many rumblings about Iowa looking for DT help in the portal, but I think it would be smart for them to do so.