Well you certainly get your Original Routing Credit when irrop'd on to a non oneworld airline. You claim that via BA after 10 days or so, either via the webform and/or by telephone.

I can forsee a potential problem given the downgrade, since in some situations AA award TPs according to the flown flights, on the basis they will refund the downgraded ticket or the ticket was an "instant upgrade", but equally some people have been successful in getting the full deal.