AA does rebook across AA-AA and AA-OW tickets. But, one is on one's own for hotels and meals. However, it will not check bags across tickets, even its own. Thus, OP will need to exit security at ORD, retrieve his bags, drag them to BA and check them in, then clear security and head to his departure gate. Would allow a solid 3 hours+ for this at ORD.

Rebooking is solid, but does mean that during high season, it may be a good long wait and in poor seats, so to be avoided unless a real need arises.