Will the StrangerVille story-based gameplay appear for all save files?

Zombies are contained in StrangerVille, and you can activate the story by picking the new aspiration that comes with the pack, and following it. Generally, all StrangerVille elements are contained in StrangerVille.

Honestly though, there won't be a lot of zombies, and most people will be normal and not pay attention to the weirdos. So if you're hoping for an apocalypse, it might be better to use that zombie apocalypse mod.