Hello! I hope you enjoyed playing, since it looks like you found nearly all the content!
There's no city-burning feature, I'm afraid. As for the survivors, if you haven't been able to find any, perhaps that's because there's none left?
The game has some somewhat obscure secrets with specific requirements; can't really tell which specific one you're missing. I'd say you can lay claim to having finished the game with how many you've found already.