You don'town the land and it reverts back to the landlord after it expires or in some cases i saw in NB. You have to pay an additional 5 rs of assessments at the end to renew your 50- 99 yr lease other wise you have only the building that is yours and I would start looking for another location to move it to if your leasehold is not renewible at the end of your term. This is why the property is below market value for simular properties at don't have this leasehold ownership on it. You Need A Good Attorney and realtor who can help you in this situation. A good realtor so you don't over pay for this type of real estate ownership and a good atorney who adress all of these issues with you before your attorney approval date is up.
Leasehold condos have only recently been authorized in Illinois and are limited to property owned by recognized 501 (c) (3) charitable organizations and municipal / public housing bodies. Leasehold condos are common in Hawaii, but rare in Illinois.
Valuation - which is not a legal issue - bcomes tricky as the property nears the expiration of the lease, when all ownership rights in the property revert to the lessor. That may be far down the road.