I would say just remove the body part from the icon. So players know it is no longer operational and to stop attacking it. It was darkening and even though it said 'destroyed' I figured I could break it since it allowed me to still target it. Either that, or when it is destroyed, make it no longer clickable to remove it as an option so turns aren't wasted attacking a broken object. Maybe make a tiny animation like a shatter sign pop up when broken / destroyed too, just as an indicator and added little fun thing?