A decent coach has little chance of making Illinois "respectable." It was so bad last time Illinois hired a coach they tried to win the lotto by reaching into into the "has-been" pile, and hired a guy who couldn't even get a Coordinator job in the pros. That was almost as desperate as Kansas hiring Weis. By the way, has hiring Les Miles helped Kansas much?
The state of Illinois is a cesspool of corruption, the state finances are among the worst in the nation and universities across the state are looking at significant budget cuts. There is little appetite to put money into the football program and there aren't any sugar daddies around to pick up the tab for the $$ needed to put the program on any kind of level even with the 2nd tier programs in the Big Ten. It used to be effective at recruiting in the Chicago metro area but not only has the quality of football declined there but, in addition to being out-recruited in the area by several Big Ten schools and Big 12 schools (as well as ND), it is no coincidence that Northwestern now advertises itself at "Chicago's Big Ten School." I personally know 2 kids who chose Western Michigan over Illinois 5 years ago.
Let's see who Illinois ends up hiring and I bet it won't be someone who is a head coach at a Power 5 school or anyone who is on a top 10 list of up-and-coming coaches at lesser schools because everyone knows Illinois is a graveyard for coaches. Like all schools of this ilk, chances are they will hire someone who has already failed and is desperately looking re-build his reputation. I don't think they even have someone like Lea, a former alum who takes a job because of his connection to the school.
As I said, Illinois is one of the 5 worst programs in the country and has been for 10 years. You could never say that about the Wisconsin program.