If its all one ticket, then Qantas will know that they have delayed you and they will know if you are going to make the connection. If not, they will be making alternate arrangements for you before the flight has even landed. You will be asked to see the ground staff for your alternate arrangements. That may mean going to the AA check-in desk for a new boarding pass for a new flight. You will not be restricted to a QF-numbered alternate flight. They will first tey to get you on an AA flight, and if no AA flights are available they will try to get you on another carrier's flight to your final destination. In my experience, Qantas are very good at doing this planning before the flight has landed and getting you to your destination as quickly as can be practically arranged.
I hope so because AA certainly are not