Contact the financial aid department and tell them. Every school has different policies about what happens next. Chicago has been the most difficult of the schools my son has applied to -- they want a letter of explanation, but say that they will not waive the form for anyone, and that the lack may affect financial aid no matter what. (As compared to say, Reed, where we sent email asking after a waiver and they said, "Okay, we'll just keep this email on file, it's fine." )
At this point, my son is aware that even if accepted, he may not get to attend Chicago because of their very strict policies about the noncustodial parent info. Again, contact the financial aid office directly and as soon as possible -- the form was due some time ago.