Okay so the whole of zombies so far was just imagined by richtofen and sam. However at the end Maxis tells Sam to make sure her window is locked and then Sam says "My dad says he has a plan" suggesting there's a problem possibly with a zombie outbreak so eddie and sam are imagining people fighting them hence why eddie says "i wish the heroes in our story were real"
To me this suggests that they will bring out a whole new zombies story if it returns and hopefully it will have a better end!
It could also mean if zombies returns in future CoD games, you'll be fighting as richtofen and sam as she says "Don't worry, we will make everything okay" suggesting that there is actually a zombie outbreak (which is why they're imagining stories about it) and maxis, richtofen and sam are attempting to stop it!
Don't get me wrong i think the ending is absolutely diabolical from treyarc however it is extremely clever in terms of making money. Think about it, zombies is a massive reason people buy CoD DLC and if they carried on this story for too long then it would start to get stale and people would lose interest. So instead of doing this they take the lazy route and do a very simple ending to a very complicated and sophisticated story. However due to the fact only around 15-20% (this is just an estimate) Of the zombies community actually know the full story, the majority of the market for zombies is still interested in getting it. Also out of the 15-20% of people who know the story, i can see very little deciding to wash their hands of it all together if they were that immersed in it in the first place!
So basically treyarc have seen that they can lose a minimal ammount of money whilst putting in the minimum ammount of effort possible. Although annoying for the zombies community, it is good play from treyarc
