Oh sorry about the confusion, there is no Game Over programmed yet. When all of the girls are "defeated" in the final version you will be presented with a final story based on what happened to each girl. Certain combinations will unlock Polaroids.
The title of the game simply refers to the apocalyptic event which ended society, it occurred 69 days before you take control of the girls in the cabin. However, in the final version the game will get harder over time, unlocking new events and possibilities. You'll notice the background outside slowly changing as the game gets harder.
I'm still working on the game intermittently, but this year I've been working very hard on Monster Girl Garden to get the Beta released on Steam. Look forward to more content updates once that is released.