“they won’t be able to come back”
That’s right. They can restrict commercial passenger travel without restricting supplies and medics. Just use military flights for that purpose. Medics can return on those flights.
The other advantage of allowing military flights is that, if it really gets out of control, they can drop an incendiary device.
Anyone that DoD sends to Liberia should also be quarantined for three weeks prior to being allowed contact with any other person prior to being allowed back into the country.