Nuclear war is probably extinction event for all / most life on earth in the long term anyways. Modern society will very likely fall apart. Because post-war society will no longer have cheap energy and resources available (we already mined those easily accessible), it won't be able to reach technological level comparable to ours.

Then all it takes is one rogue asteroid, or supervolcano eruption. Advanced society might be able to prevent it. Middle-ages one? Not so much.