I guess it depends on your definition of society- they wouldn’t have a functioning government for a while, but the people surviving would still be Iranian and depending on whether they’re Kurdish, Persian, or other, might still have loyalty to the idea of an Iranian state.

Okay this one is fun and much more my area of expertise. You're getting at the core because it is something that is very difficult to determine. The Roman Empire is a great example, we can talk about just the west for now. Roman Britain was abandoned by the Roman's, and yet archaeological evidence shows that they still tried to live like Romans or at least the elites did. Historical records show a clear point at which the Roman Empire left, but when did the elites and people stop considering themselves Roman? They did eventually stop, and that was due to being cut-off from the empire.

Then you can look at the Bronze age collapse where whole civilizations just ceased to exist. Certainly the people persisted, but few states survived in tact. People still lived their but their civilizations ceased. They spoke the same languages still, but many cities across the Mediterranean region stop inhabited. By the time written record returned new states had formed and material culture changed. We know logically the people themselves existed in continuity but their societies ceased.

Maybe this is getting to into the weeds and not appropriate here, but this is my field and I've dedicated a lot of time to it. So the short answer is it is nearly impossible to draw a line, but societies do collapse even when the people persist

Radiation typically spreads through weather as its lifted into the atmosphere. Mountains notably break-up and can contain weather fronts. It will also inhibit the aresolization of radioactive dust.

Look into how mountains impact weather and the movement of air. I'm not claiming it will 100% contain radiation spread but it will help limit it.

Remember it is a function of time as radiation naturally decays over time. This isn't Chernobyl, nukes are designed around isotopes that degrade faster.

But yeah Pakistan and Russia would likely feel the effects to some degree. Is Saudi Arabia a nuclear state? They would feel it too.