Legal Question in Real Estate Law in Illinois

It depends on your lender. They may approve the loan based only on your credit. You may want to initiate the conversation before it becomes an emergency.

Ideally, you would qualify on your own, whether for another loan or some sort of modification of this loan. If not, you can see if another qualified party will co-sign. If not, then you may be without an alternative except to try to sell the property to avoid losing it.

That said, the co-signor needs to consider the ramifications if this will force a default. In many co-signing situations, the co-signor is the more financially stable, meaning the forcing of a default could impact the co-signor more than you (lender may enforce a deficiency against the co-signor; co-signor's credit may take a greater hit).

Ideally, work through all the options with a local real estate attorney as far in advance as you can (now). Perhaps there is a common ground that can be reached that will be to the advantage of all concerned.