I'll soon be taking a flight from Madrid to Victoria Falls, with a scheduled 1-hour connection in JNB. That will be ample time if the incoming flight is on-time or close to it (carry-on bag only, traveling in J so among the 1st off the plane, and transiting so no immigration/customs). However, the incoming flight from Madrid is frequently delayed.

MAD-JNB is operated by IB, and JNB-VFA is operated by BA (Comair). The ticket is an award ticket issued by AA.

If I misconnect due to a late incoming flight, whose responsibility is it to get me to VFA -- IB or BA? Is there a rule regarding the time period to get me to VFA (for example, if the next BA flight is in 20 hours, but another carrier's flight is in 4 hours)?