From what I can find, there are 19 seniors who currently play at least 40% of minutes who will be graduating. Below, I've got the seniors >40% in bold, other seniors, other guys mentioned on various mock drafts who could leave early in italics, and current recruiting class rank:
Michigan:
Jon Teske, Zavier Simpson, #4 recruiting class (1 5-star, 3 4-stars)
Illinois::
Andres Feliz, Kipper Nichols,
Ayo Dosunmu #10 recruiting class (1 5-star, 1 4-star, 2 3-stars)
Wisconsin:
Brevin Pritzl #22 recruiting class (2 4-stars, 3 3-stars)
MSU:
Cassius Winston, Kyle Ahrens, Joshua Langford,
Xavier Tillman #28 recruiting class (2 4-stars)
Purdue:
Jahaad Proctor, Evan Boudreaux, Tommy Luce, #31 recruiting class (2 4-stars, 1 3-star)
Indiana::
Devonte Green, De'Ron Davis,
Trayce Jackson-Davis #35 recruiting class (2 4-stars, 1 3-star)
OSU:
Andre Wesson,
Kaleb Wesson #44 recruiting class (2 4-stars)
PSU:
Curtis Jones, Mike Watkins, Lamar Stevens #47 recruiting class (4 3-stars)
Minny:
Alihan Demir,
Daniel Oturu #54 recruiting class (2 4-stars)
Iowa:
Ryan Kriener, Bakari Evelyn #55 recruiting class (2 3-stars, 3 lower ranked)
Rutgers:
Akwasi Yeboah, Shaq Carter, #59 recruiting class (3 3-stars)
NU:
AJ Turner, Pat Spencer #64 recruiting class (1 4-star, 1 3-star)
Maryland:
Anthony Cowan, Michael Hurt,
Jalen Smith #91 recruiting class (1 3-star)
Nebraska:
Haanif Cheatham,
Matej Kavaš,
Cam Mack #91 recruiting class (1 3-star, 1 lower ranked)