The stories of fallout have been told in the games many times we all know them.
What happens when the heroes arnt there to save everyone. Sure the brotherhood of steel still blows up maraposa military base, but no one stops the master.
With the mutant problem the ncr never spreads to meet the desert Rangers.
The desert Rangers deal with Cesar’s legion alone, while dealing with the khans.
Up north the robots are still unleashed by the roving mutant horde and the iron circle is caught in the middle.
The enclave just bids it’s time amassing its forces for there rise to power.
Although elder Lyons, was tried and sentenced for treason against the codex, the new elder has taken no time securing the brotherhoods position in the capital wasteland. Elder Harkness fears her efforts maybe in vain for she know what is heading east, general Attis. All she can do is hope she’s strengthened there forces enough.

And here you are the Heros of this dark tale tied up in the back of a wagon waiting to be sold.

Below is a link to the d20 modern srds:

Dark times in the capital wastland