It could be interesting to have a way to repair the Factories from rubbles to functional again. So, for example, biters destroy a factory. It leaves behind a demolished-Factory that is not the target of any biter attacks. (If that's even possible) You, as the player, may either destroy the demolished factory to use the space, or repair it to use it again.
Also, if that's a thing, it also allows to spawn broken factories instead of alive so that player need to repair them before use.