As far as I know (in terms of the comics) they're still there and loads has happened in the comics that hasn't in the shows yet. For now at least it's moved on from the "constantly on the move" stuff of the earlier seasons... they don't really consider Walkers to be much of a "threat" at this point because they're so good at taking them out, more like any other dangerous animal that they have to deal with when they leave a place that has walls. There are a LOT more human characters now (towns with hundreds) and it's all mainly centered around human threats with the walkers being more of a "backdrop".
The show isn't REALLY a Zombie show any more to be honest, so much as a general post-apocalyptic show where "Zombies" happens to have been the world ending event. It wouldn't be "realistic" any other way to be fair. They've been living and surviving with walkers for (I'd guess based on Judith's apparent age) about 2 - 3 years now so anyone still alive would definitely have adapted, and would be focussed on trying to rebuild a home and society rather than raw survival.