1up.com has published an informative article on the reality of the Fallout universe:
In very general terms, Dr. Miyamoto says the world would be livable. "Most of the isotopes would be gone and the half-life would have expired, so they would be safe," Miyamoto told 1UP. Most major fallout products have relatively a short half-life as compared to the dozens of years before vault-dwellers explore the wastes. On the other hand, it's hard to predict how a body might react if sealed away in a vault, as the plot of Fallout games often requires. "People are exposed to radiation every day, normally, going outside," he said. "You're exposed to more radiation living in Denver [Colorado] than living in New Jersey. So to compare to someone who has never been exposed to radiation, we don't know. What we do know is that the body has innate repair mechanisms. Would those mechanisms be impaired by not having them stimulated at a young age? That scenario doesn't actually exist, so just as conjecture: probably not. Our own body's defense system would be intact and passed on genetically from our parents."
And while irradiated water is a serious threat in Fallout, and even a major plot point in Fallout 3. Miyamoto suggests that wouldn't actually be much of a threat. "I don't think any of the contaminants would still be residual, so I would think the water supply would be relatively safe unless you're near a highly radioactive area."
Fallout games do include various radiation hot spots, however. While most of the land is fairly safe, a trip to certain areas gives radiation poisoning extremely quickly. These could be areas that were more directly impacted, or still have remnants of uranium or plutonium. These pose a serious risk that's portrayed with at least some nod to reality. "Let's say you were near [direct exposure]. What protects you? Substantial shielding, and distance." Miyamoto also mentions that time is a factor, so if exposure were absolutely necessary, you would want to get the job done as fast as possible.
And if you don't take those precautions, the grisly effects are realistic too. "The most sensitive part of your body is your bone marrow. So even if you were exposed to relatively low doses of radiation, that can kill you unless you get a bone marrow transplant. You would probably survive two weeks. If you're exposed [to a] slightly higher [dose], you'd develop classic nausea symptoms, like vomiting and diarrhea. Those people might survive with a lot of IV fluids but then they'll die from the marrow toxicity. If you're near a very high dose, and you're not protected, you're just toast."
Survival depends on how closely the inhabitants are to the bombs' epicenters. Towns are generally placed outside of radiation hot spots, which is conceivably possible. "There would be other things that would be longer acting -- radiation in the plants, for example. After a nuclear holocaust, it depends on how close these people are to the centers where this happened. If they're coming into highly radioactive areas, they could all just die. But if they're on an isolated land away from these centers, it's possible after the fallout is gone, they could recreate society. They could repopulate the planet."
Of course, nuclear radiation is only one of the threats facing wasteland wanderers. As any post-modern monster flick will gladly tell you, man is the real monster. Even if humanity was physically capable of repopulating the planet, would we see the relatively sophisticated social structure portrayed in the games? These were questions for Dr. Cerulo to lend her expertise on human behavior.
The propagation of small, self-sustaining agrarian societies is fairly realistic, according to Cerulo. "People tend to localize their behavior when these kinds of things occur," she said. "So if there were a complete wipeout of the central government, we'd see lots of local communities empowered by those people bonding together."
Hostilities between groups would rely quite a bit on how much time has passed. "Each of these small communities would be trying to figure out how to sustain themselves, so the tendency to look outward would come way down the road when the local community was stabilized," Cerulo said. A longer timeline means more warring factions. "People want to maximize their resources, and sometimes they do that in a competitive fashion. These communities might merge their resources, trade on the basis of strengths and weaknesses -- or you might get some people who use violence or force, just as we see now. For the game's purpose, it's more fun to go to war, but you'd see a combination of both. Even in war, I think cooperative strategies would dominate."
Part of trading or warring over resources, though, is the availability of food. "Some groups would be involved in trade. Maybe some places are more adaptable to farming, and others aren't. Some places might have access to crude machinery, so they'd be trying to find the best ways to help each other."
In establishing trades, the Fallout universe relies mostly on a form of currency in the form of bottle caps. This, according to Cerulo, is fairly realistic as long as it's an agreed-upon standard. "Typically, it's the centralized government that figures out how to make currencies translate," she said. "[Caps] could be functional; there's nothing inherently valuable about a paper dollar. These things are all defined by an agreed-upon scale. It could be bottle caps, pieces of thread, stones -- if somebody is able to define a system that gives a value per cap, and if there is the ability to have a set number of caps that you can create value relative among groups, it really doesn't matter what the substance is."
And though most of the racial tension seems to go towards ghouls, some amount of bigotry would likely stick around even in the face of armageddon. "If there is a memory of a thousand years of history and hatred between certain ethnic groups, it seems unlikely that it would be completely wiped out in favor of a new group," said Cerulo. However, she says it is "very realistic for some group with a distinguishing characteristic to be scapegoated."On the whole, Fallout seems to portray the broad strokes of armageddon's aftermath accurately -- both scientifically and sociologically. Next time you walk into the wastes, you can consider it practice for what to do if doomsday ever really does happen.”