interesting design, but nonsensical ludo-narrative combination. 0% can be caught when there are still buildings on screen. I see this is "by design" in a response to another comment, but it makes NO SENSE. the statement even says, "no where left to live" so what are those buildings? useless blocks of concrete that are unsuitable for living? why were they built?
and if 100% were when the city is too big to be destroyed, then why is it i can burn whole sections down with one click? wouldn't it really mean the city is too interconnected and will burn completely down with one fire? then you only have to have one lose condition, the city burning all the way down, leading to the, "why burn a building?" question, which could easily be answered by changing it to a turn based game, can move so far, having to jump to another building to keep your flame alive, but you don't want all your buildings to burn down at once, because that would be game over; of course keeping the burn adjacent buildings code. then just put a signal to show where buildings will be placed in the next turn. instantly 100x better.
Don't use your story as a blanket to cover poor game design implementation.