There are various types of ZombiesThis is why the stories differ so much on creation, reproduction, and extermination. A necromantic-raised zombie is different from a virus-raised one is different from a construct-raised one from a pharmacological-raised zombie. Woe to the person who confuses a magic-modded undead super soldier for a stumbling victim of drug-induced stupor.
If the world is taken over by slow zombies, everyone will be fine. But if fast zombies take over, humanity is screwed.Slow zombies - only a few people taken by surprise and idiots will get killed, because they move so slow. Fast zombies however - those are a bit harder to escape.
Even if every viable corpse was to suddenly reanimate, and they were fast, zombies won't be the end of the world.When you see a zombie movie, the individual zombies are no threat; the problem comes from the outnumbering humans. It's a dozen humans against billions of zombies with society in ruins. So if it is billions of zombies against billions of humans with working infrastructure (including well-trained armies), then things start looking less hopeless. And if they are scientific zombies that start with only one...