When check-in is opened for a flight, the pre-allocation seatmap becomes useless anyway, as it is not connected directly to the check-in system. At the point of opening of check-in the seatmap will get transferred to the check-in system, and from then on the only way to assign a seat is to check-in. However I think there is still a way to check-in by phone (not sure, haven't used this for years) but likely not ex-ORD. And of course OLCI, maybe also unavailable from ORD?