Gut feel.
He quit on his high school team, tried to quit UM after his freshman season (coaches talked him out of it) then quit mid-season and most importantly, mid-semester. So in order for him to play at another D1 school he'll have to make up the classes he didn't complete this semester at UM and be a full time student at Illinois for one full academic year before being eligible to play again.
Had he stayed at UM he would have been the marquee guy in 2019 and been in prime position to get drafted in the 2020 draft. Now he'll have to do what I listed above then play for Illinois in 2020 and go into the 2021 draft. I will be very surprised if he can hold up through all of that. Just my opinion.
Had he transferred to a lower division school he could have played in 2019 and entered the 2020 draft but instead he chose Illinois so he has to sit out 2019. Questionable move.
I can foresee a scenario where he just uses Illinois as a practice spot in 2019 then declaring for the 2020 draft after not playing the 2019 season. He'll go undrafted but will likely get a UFA opportunity with some NFL squad. But that would mean he never plays another CFB game (my prediction). This is the most probable outcome IMO.