OK here my deal after betting the game why cant you continue playing the game after the ending you are suppose to get a special perk if you play it all the way thru hardcoe...?

The reward for beating it on hardcoe is an achievement and the dubious respect of the forumites. Not a perk.

You can't keep playing after the ending because all stories must end. Otherwise, how is it an "ending"?

-Nukeknockout

Too many possible endings for it to just continue after the Battle of Hoover Dam.

And all you get is an Achievement/Trophy, nothing more, nothing less.

Just load back to a save before you committed to go to the dam. And you can continue exploring and doing side quest