They will and it's a good thing. It gives object value and encourages trading between civilizations on all levels of government. If your county is in a shortage of iron you may need to trade steel to another county for it. As for worldwide extinction of a resource I don't believe so. I think somewhere will have it and if not an event may restore a bit to the world like a meteor shower or the ability to dig deeper into the earth discovering new mines and what not. Maybe a new island.