for those of you saying maybe they would release it as a $30 disc, i think this is a VERY unlikely scenario. in case you haven't bought any AAA video game titles since the 90s, they all cost $60. so as mentioned above, either its gonna be a full priced game by 3arc "COD:Zombies", a part of the next 3arc game. or nothing at all
also, it is important to note that at any given time in COD:BO2, roughly 1/4-1/3 of the players are playing zombies. if you don't think they can support their own game, i think you are wrong. especially when you could make a zombie game with the SAME fucking multiplayer as already exist, just with the zombies as the campaign mode (and general design aesthetic). i think they will kill the BO story line and start the Z. instead of an army load out (m4, body armor, rocket launchers), its more like an apocalypse load out (remington870, football pads, moltov cocktail). it would be bad ass.
i also think they should make zombies multiplayer (separate from single-player campaign mode) with a character you make. similar to loadouts, but you only get to choose starting pistol, and one "trait" that is analogous to perks (extra health, faster sprint, more damage) and character customization (think TF2 hats... for zombies)