I found one highly comparable situation at another program (with a very much hated head coach) that had underclassmen as leading contributors to see where Illinois might project next year assuming everyone important is back.
2016-2017 Auburn: Finished 18-14, ranked #82 on Kenpom
Leading/notable scorers:
(FR) Mustapha Heron - 15.4 pts
(FR) Jared Harper - 11.4 pts
(FR) Danjel Purifoy - 11.5 pts
(SO) Bryce Brown - 7.5 pts
2017-2018 Auburn: Started at #46 -> Finished 26-8, ranked #23 on Kenpom (4 seed in NCAA)
Leading/notable scorers:
(SO) Mustapha Heron - 16.4 pts
(JR) Bryce Brown - 15.9 pts
(SO) Jared Harper - 13.2 pts
(FR) Chuma Okeke - 7.5 pts, 5.8 reb
2016-2017 Auburn: Finished 18-14, ranked #82 on Kenpom
Leading/notable scorers:
(FR) Mustapha Heron - 15.4 pts
(FR) Jared Harper - 11.4 pts
(FR) Danjel Purifoy - 11.5 pts
(SO) Bryce Brown - 7.5 pts
2017-2018 Auburn: Started at #46 -> Finished 26-8, ranked #23 on Kenpom (4 seed in NCAA)
Leading/notable scorers:
(SO) Mustapha Heron - 16.4 pts
(JR) Bryce Brown - 15.9 pts
(SO) Jared Harper - 13.2 pts
(FR) Chuma Okeke - 7.5 pts, 5.8 reb