Or until another nuclear war?

I don't think the NCR will ever take over the entire country. On the West Coast we have the NCR, on the East Coast we have the Commonwealth, but we know of no nations in the mid-west that have formed. I'm sure there are, however, we just haven't heard about them yet. And if and when the NCR ever reaches the mid-west, they will surely put up a fight.

The Commonwealth, from what we know, sounds like a damn interesting setting. It's a nation whose government is more concerned with advancing it's own technological prowess than the well being of it's own population. It creates androids for the purpose of enslaving them, and has an entire branch of the police dedicated to hunting down any that try to escape, no matter how far they go. Assuming they put that advanced technology to use in their army, they would surely put up a good fight if the NCR ever managed to reach the East Coast.

It took 600 years from the decline of the Roman Empire to the rise of the Renaissance. So 600 years is the meterstick for this kind of thing, though Rome didn't collapse in two hours like the world did in Fallout.

But I highly doubt the world will ever be "Normal" again. For starters, the whole point of the Resource Wars that lead into the Final War was battling over Earth's few remaining fossil fuel resources. There's literally not enough left to restart Civilization as it had been.

Actually civilization is restarting retardedly slow in the Fallout Universe circa FO3/NV, we might not expect cities, reliable long distance travel and so on. But it doesn't even show villages being built new, everyone lives literally in the garbage of a past civilization. How about chopping some trees for houses? Painting your shacks? Plastering the outsides of them? Cleaning up the damn skeletons everywhere? That's basic stuff for which you don't need advanced technology, ffs, they've been doing it for millennia.
I know they're going for some frontier feel, but they've done a [censored] job of explaining it. Suspension of disbelief only goes so far.

Of course there is no real way of knowing without nuking the planet.

*sigh* Does anyone pay attention in school or read any more? The world has gone through apocolypses with what we would consiter frighteneing regularity. We're spoiled because we haven't experienced one in known history. Only about ten thousand years ago the northern hemisphere was scraqed clean and frozen solid yet, as the ice melted, life came back as lush and diverse as ever. Yeah, okay, we lost most of the cast from Ice Age but that's been blamed mostly on the native american population. If I remember correctly, we get devastating volcanic events every seventy five thousand years that clean the world too. Then there are the rocks from above. Many thing go away permanently while many things adapt, evolve and be fruitful.

The Fallout game doen't allow for the insignificant, in game terms, to stand out so out of sight out of mind. First, I don't see the radioactivity from the bombs as infinite. Even in Fallout terms the background radiation is nil except in concentrated areas especially water. What is it with water that it retains radioactivety more than any other substance? Are the oceans totally irradiated too? With Project Purity this will become inceasingly reduced in the Washington area and may lead to replication in other high impact regions. If the Wanderer releases the seeds of Oasis, Washington and the rest of the east coast can expect all sorts of vegetation in decades rather than centuries which is expected anyhow. That's a big jump that our world didn't see a hundred centuries ago, 'Insignificant' animals we don't see in the game will fill the forests and fields just like after the ice age.

I hope Lyons is the future of the Brotherhood at least on the east coast as well as groups like the Rangers. The Wanderer pretty much single handedly cleans out the super mutants and several other threats so reclaiming the Wasteland should be so much easier. The Washington Brotherhood can become the foundation for technical applications for the people allowing people to rebuild society. Once again, check history. Mankind, with the right people and incentives go from scraping unforgiving dirt, dying regularly while still young, and barely thinking beyond the next meal to in centuries. This is without the benefit of working tech artifacts. By 'normal' we probably mean a society that understands and recreates the technology at the beginning of the war plus living standards for health, education and such nearly equal.

Just like the human body many wounds will heal while there may be some scars. More importantly will be the mental traumas of the war and its aftermath that will never let the world go back to whatever they had in the past. If a person from the pre-war days visited the rebuilt future it would be alien to them.