If their leaders are destroyed by the Courier, the Fiends scatter throughout the wasteland. Without the organization of Motor-Runner, Cook-Cook, Violet, and Driver Nephi, they were easy prey.
If never weakened by NCR, the Fiends stage an attack against Camp McCarran during the second Battle of Hoover Dam. Though NCR repulse the Fiends, they both suffered heavy losses in the process.
If the NCR retreat, the Fiends stage an attack against Camp McCarran during the second Battle of Hoover Dam. The Fiends overwhelmed many of the troopers before Mr. House's Securitrons could deal with them.
If anarchy reigns after the second Battle of Hoover Dam, fiends overrun Camp McCarran and in the months that follow, the Fiends assert dominance over outer New Vegas.
If weakened, the Fiends attack McCarran during the second Battle of Hoover Dam. NCR repulse the attack with minimal losses and, in the following days, destroyed the remaining Fiend leaders, breaking their power forever.
If the Legion wins at the second Battle of Hoover Dam, Caesar, unimpressed with their performance and their dependence on chems, has the Fiends exterminated.
If Mr. House asserts control over Outer Vegas, and the Fiends are weakened, his Securitrons eradicate the remaining Fiends entirely.
If anarchy reigns after Hoover Dam and the Fiends are weakened, the Fiends attack Camp McCarran during the second Battle of Hoover Dam and, despite suffering heavy losses, overrun it. They continue to be a nuisance throughout Outer Vegas, but never establish full control over the area.