Zombies don’t really work like that in this world. They evolve and adapt faster than we do, and there’s no evidence they rot… quite the contrary, they seem to get stronger and more powerful over time. Mutations also don’t work like that: it’s not clear if, or even how, mutated humans can breed.
The game doesn’t take place in the distant future, it takes place “next year”.
The difficulty of balancing necessary post apoc staples like psycho raiders with the likely IRL banding together of surviving factions against a common enemy was handled a while back by writing in blob psychosis, which also conveniently explains the behaviour of a lot of players.
Roughly 1/1000 to 1/10,000 people survive to game start. If you consider how many players make it past a year, even with the benefit of metagame knowledge, you can guess how many NPC’s might survive that long… By the end of year one, when people have finally had some time to sort things out, the living human population of the planet is probably in the tens of thousands, and many of those are transhumans that are likely not viable to have babies.
The majority of survivors would be people who have hidden in bunkers and shelters though, probably outnumbering high powered risk takers at least ten to one. So that means there are maybe a couple thousand player level survivors after a year or so, at most.
If those survivors eke out a few safe spaces on the planet, they can likely figure out a way to live out their lives in peace. There’s no taking things back. Even that’s a tall order, but it’s achievable. There’s no way a population the size of a small city is going to have the skills to eradicate an infection of billions of monsters, let alone one that continues to adapt to defeat their weak points
