Buying a property with occupied illegal unit

[Akil Mitchell]

Hello, looking to get into my first house hack in Chicagoland area. I came across a 2-flat with a basement that has been converted into garden unit with 3 bedrooms and kitchen and bath. My realtor found the city building inspection report which details that the unit needs to be de converted as it cannot be brought up to code. This unit currently has tenants living in it. My question is can I purchase this property, renovate the top two units and just leave the basement as is? Or will I be forced to pay to de-convert the unit before I can do any other renovations? Illegal basement units seem to be very common in this area.