I agree. Defrosting/defogging capability will be non-existant, and the car won't be very safe in the winter. Even opening the window might not be enough if you're carrying more than yourself.
Heater core replacements were common on cars I owned like my old Camaro, and it was a half hour job. Parts were cheap, access was easy, and things were pretty straightforward. Bloody Germans sometimes just make things too complicated for their own good.
1998 C230 "Black Betty"