I'm pretty sure the implication is that the Courier takes control of everything. That's kind of my problem with the whole ending. The courier is a dictator. They control the securitrons, so they are in charge. Even if they die, or leave, or whatever, then whoever controls the securitrons next gets to be in charge. It's really no different to the house ending, or some hypothetical ending in which Benny succeeds, except to the degree that we can imagine that our personal courier would be a nicer person than those people (would they really though, how many people did you kill in Fallout: NV?)
NCR is a shitty democracy. But it's a shitty democracy in a world where democracy is a ridiculous and impractical experiment (bear in mind, the pre-war USA in the Fallout universe was not a democracy). It's a bad ending, but it's still the best ending we are offered.
