Who says the same characters need to be used? Maybe this is the end for these characters, but there are still unanswered questions. The new characters could be other people significant to the story. In the first few new maps, they may seem completely separate from the story, but as the "new" story goes on, it links with original story adding new depth. Now, almost all of what we know about the Zombies backstory comes from radios. These maps could help us better understand the story as well as add new elements. They could take place during WWII like the original Nazi Zombie maps, as there is a chance the next Treyarch game will be WWII. If the next Treyarch game after that is a sequel to BO, then that's when the stories will link. Another theory is that the new Zombies maps don't feature the original characters. The original Nacht Der Untoten, original Verruckt, "Five," and Call of the Dead didn't feature the original characters as playable characters although in Call of the Dead, they are featured in the Easter egg. Perhaps the new Zombies maps will be like this, independent maps with almost no significance to the story. However, this would be boring. My final theory is that the four characters end up going deeper into space. Perhaps they find a rocket that takes them to Mars (Yeah, it seems a bit far fetched, but there isn't even a massive base on the Moon now, much less in the 1960s). However, I don't know where the story would go from there. Maybe they find an ancient Martian teleporter, shoot a Wunderwaffe in it, and get sent through time and space to pre-explosion Earth. Or better yet, instead of going to Mars, they simply rig the teleporter on the Moon to send them back through time to before Richtofen blew up the Earth. I think my first theory is the most likely. Maybe these characters aren't entirely done. Maybe after the new part of the story with new characters, the old ones will be revisited and the two sets of characters will meet. After that, the Zombie maps may be released alternating between the two sets of characters. I highly doubt that Zombies is completely over. I think my first theory is the most likely, although it would be cool to see them go to Mars. That however, is least likely.