Oil (and coal, which is less topically sexy but historically more significant to industrialization) is the big problem, though rare earths and other materials that see use more in trace than in concentration could also be an issue. If you're a medieval-level smith, you probably wouldn't care too much whether you're getting your Fe from bog iron nodules or from the melted skeletons of god-towers in the ruins of Ellae-that-Was, although certain types of bottleneck event could make the latter problematic for a time.

Still, I'd be willing to bet at even odds that that wouldn't be a showstopper if it came to it.