True.But there are societies with people who still remember that.I would die in Warsaw,just like other polish city dwellers,but part of villagers would survive.They could even keep working trucks or small planes.Certainly they would made tools from iron.Yup.
Indigenous peoples (like the Sentenalese) would be fine. Everyone else would be screwed six ways to Sunday because we don't know how to do what they took for granted. Can you start a campfire without an ignition source like a match, lighter, or flint-and-steel?
In theory I know how to do it using a dry pointed stick and dry piece of wood. In practice it would be a long, cold, and dark night because I have no clue how find pieces of wood appropriate to the task.