I believe, that since the map name is "Origins" that this is obviously the beginning of zombies, we find the O4 in Normandy battling the forces of the undead, and trying to save "Samantha" from Agartha. Tho my theory may seem far fetched, this could all be trickery from Samantha, due to the fact she was trapped in Agartha......she was obviously trapped in their for a reason. That reason being that she is evil. When Maxis and his crew started on excavation site 64, the awakened an evil, Samantha, and since Maxis awakened Samantha, she kept him in mind. Made up a lies to tell the O4, so she would be released. If you note, Richtofen doesn't seem to buy the story of hers. In the ending cutscene, we see that Samantha has possessed the daughter of Maxis, whose brain was transplanted into a newer host due to his past zombification. Funny how Samantha chose to stay close to maxis? I think not! She knew that he was very prominent, and could manipulate him to get exactly what she wanted, which was revenge for being trapped in Agartha for so long. So I believe that the ending cutscene is in or on the outskirts of the Der Riese facility, and our story which started in W@W is about to begin.