https://www.pcgamer.com/fallout-new-vegas-mod-adds-a-post-game-that-reflects-your-choices/

Fallout: New Vegas, normally reactive, stops short of letting you continue the game and enjoy the ultimate consequences of your actions once the credits roll. It just ends. With mods, you can find a way around that and hop back in, but you'll find a world in stuck in the moments prior to the ending. Not so in the new FPGE mod, however, which creates a functional post-game ending. 

With FPGE, you'll find the world reacting to your big decisions when you return to Nevada. Factions can be wiped out, others might conquer regions, and the Hoover Dam can be taken over.