Originally Posted by
NYC Flyer
The obligation rests with the carrier triggering the missed connection, not the carrier you are connecting to. If the delay involves an AA flight, AA bears responsibility to get you to your destination.
While that is the general policy, AA is unique in that it protects connections AA-AA, AA-OW and OW-AA. Thus, in the example of separate tickets QR-AA, AA would handle a reroute, while QR would not.