If you take all the rules of this universe in account - like "all humans turn, no matter how they die", "walkers do not weaken/starve/die off over time", constant fighting between survivors for various reasons and enormous zombie-to-human ratio (as mentioned here, it is 5000 to 1), it seems almost impossible for humanity to ever win in this scenario.
Even if humans somehow manage to survive with scarce resources and start clearing the walkers from the face of the Earth with little to no casualties, in the end all of them will still turn simply because of dying for natural reasons. Reproduction won't be high enough - every next generation will be smaller than the previous due to highly dangerous environment and constant zombies reinforcements, and eventually humans will just go extinct.
Was it the author's thought from the beginning - that this really is the end of the world and that humanity's doomed or are there some possibilites for winning and rebuilding in this situation?
Edit: So, I forgot to clarify that brain trauma is an exception in "all humans turn, no matter how they die", but still - for walker reinforcement to stop you'll need to crush every single skull of a recently dead person, which isn't always possible (remember those stories when "we had a camp, but one of us got bit or died, we overlooked it and boom - everyone's eaten" - there are always risks).
As for "weakening over time" - yes, they do become more soft and even "jelly" (as evidenced in TV series) over time, but what I meant was this: zombies do not lose any offensive capabilites, they don't become slower or less deadly in 1/5/10 years, and with all "zombie rules" like no need for food, oxygen and so on in order, they're basically immortal (before they get an axe to the head, that is). And the main problem - all zombies need to be eliminated, waiting it all out won't work, and eventually everyone remaining will turn anyway (if no cure is produced), so there are quite few, if any, winning scenarios.