When they leave the country, they have no due process rights for return. Current law already forsees:
Even a permanent resident (green card holder) isn’t safe from being found inadmissible. If a permanent resident departs the U.S., it’s possible for him or her to be found inadmissible upon return. This situation might arise, for example, if the person had been gone from the U.S. for too long, had committed a crime, had developed tuberculosis, or had begun receiving public assistance since receiving the green card.
Further, whatever due process rights such a person might have when the reach the US have NOT been eradicated in that EO - the one section that could bar them also allows for the Offices of the Secretaries of State and Homeland Security the authority to grant waivers on a case by case basis - which directly implies that there is a path to entry for these people.
Lastly, the “point” is, entry to the US for non-citizens is a privilege, not a right. Rights can not be denied without due process - privileges are granted and rescinded at will.
The courts disagree, and I don't mean the 9th Circuit. Constitutional due process rights apply to everyone in the country, not just citizens. Aliens outside the country have no constitutional rights. Everyone inside does. Disagree with that if you like, but argue with the courts, not me.