Rand does mention what happens to the violators of the Directive: they go rogue, become villains, form gangs that roam the wilderness. That is the only course I could see. Screw starving to death, take what you need, and if you have to kill a few “authorities” to get it, so what? Even if they eventually kill you (I think that is why the military is moving around so much in the novel, hunting gangs/raiders), it’s better that going out like a wimp.
The plan executed by Galt, D’Anconia, and Danneskjold is to bring the world to its knees by being as stupid as society claims to desire. When John Galt says he plans to return to New York, they try to talk him out of it by describing some of what they expect to happen. The story mentions gangs of raiders only a few times. None of the characters ever encounter such types. Hank Rearden will encounter something like them later (I'll avoid the spoiler details) but the antagonists are not a raider gang. They had other motives.
Part of this is Rand playing black and white. Individuals are good, collectivist government busybodies are bad. It's difficult to portray the rugged individualist as the good archetype when some of the rugged individualists resort to armed crime for survival. But Danneskjold does the same thing and Rand uses him as irony; the brilliant philosopher turned pirate because society would accept nothing else from him. Mr. Spock was hardly the first person to realize that, “In an insane society, a sane man must appear insane.”
Rand could have explored this and added some interesting characters and subplots to the story. In all honesty, I wanted to murder James Taggart around page 100. I didn't need to read about the fiftieth time he used influence peddling to stick it to somebody he didn't like, which was anybody. The reality of the world coming down on people's heads is gripping drama. Think of the description of the wreck in the Taggart Tunnel. It's one of the most captivating parts of the book. The collectivist mindset kills people. Imagine if Rand knew about Soviet adventures with nuclear submarines and power plants.
And not all of the black market in such a world is evil. In a world where boot-licking is the most marketable skill, some will be better at it than others. In any economy, some people will hoard the benefits they receive and some people will share them. Cheryl could have been such a character. It would have been interesting to see how bureaucratic inertia frustrated her efforts. This theme was played out in The Fountainhead. Catherine, Ellsworth Toohey’s niece and abandoned bride of Peter Keating, becomes a miserable social worker, of the type that enjoys knowing that others suffer, and feeds on making them suffer some more. But she didn't start out that way.
The more I think about it, the more I believe that are there other, and equal, themes to Atlas Shrugged besides the stupidity of Karl Marx. Rand lived that lifestyle herself. IMO, the best part of AS is quoted in my profile.