I am not trying to critical, nor am I familiar with AA/US policies regarding this type situation for safety reasons since there was only one pilot at the time but as a Paramedic I am curious why if he was in fact flying the plane, found to go unresponsive that help was not summoned immediately and he removed from the cockpit so that resuscitative efforts could have begun.
All commercial airliners are equipped with automatic external defibrillators (and flight attendants who are trained in their use) in addition to medical equipment. For someone who has gone into Cardiac Arrest the first 4 to 6 minutes are "make or break time". Good CPR, with assistance from an AED assuming he was in a shock able rhythm may be all it took to revive this individual.
The rumor that a nurse attempted to revive him seems unlikely if no one on the plane knew what was going on until they landed. My assumption if he was attempting to be revived would be that it was done in the floor of the forward galley.
I would love to know more if anyone has credible information.