Found a mod that allows you to continue to play NV after the ending. Also, the ending that you get will transform the gameworld accordingly.
Mod author said:After two weeks, Hoover Dam is taken over by the respective faction and the fighting stops, the Kings will get eradicated by the Legion, if alive, the Brotherhood of Steel will take over Helios One and patrol the roads, and the Great Khans will evacuate their camp, taking everything with them. This is only a small portion of what can take place however, and there are a massive amount of things that change based on how you play.
Not only this, but dialogue has been changed to represent whatever endings are chosen, for instance:
"We'll show everyone that these are our new territories!" - NCR citizen. This is no longer shown should the NCR lose, why would they prattle on about this after they lose?
"We won't go quietly, the Legion can count on that" - NCR trooper. No longer shown should the Legion fail miserably, they wouldn't exactly need to worry about that after they win would they?
This is only a small selection mind you, but it's just a demonstration on how much love I've poured into this mod. I've played New Vegas for years and loved it ever since, so I thought it only appropriate that the game had a proper ending. I've considered nearly everything, so worrying about missing content or otherwise shouldn't be an issue.