I've had the exact same problem as you... I had my European/African segments as LHR-DXB-LHR-ACC-LHR-JNB... AA RTW desk actually caught the mistake after it was ticketed, and they called me... basically they told me that if I had to re-issue the ticket, the ACC routing would be invalid... luckily I didn't have to change the dates, but from that experience, I learned to ticket RTW tickets with open segments instead of dated....

So I take it that the reservations on the ACC segments have been cancelled already? You might want to try to call up BA and tell them to book you back onto the flight.. just tell them that you have an open ticket.. don't think it matters if your ticket already has the proper date on it....