If the dog has travelled to a high-risk rabies destination without obtaining a Certification of US-Issued Rabies, their re-entry into the USA will be subject to the same rules as a foreign-vaccinated dog.
This doesn't mean the dog won't be able to return. The will need to meet the following requirements:
Rabies serology will be required from a CDC-approved laboratory. The blood sample for titer must be drawn at least 30 days after the dog’s first valid rabies vaccination and at least 28 days before entry to the U.S.
Approved Rabies Serology Laboratories for Testing Dogs
Apply online for a CDC Dog Import Permit.
Dogs must have a reservation at a CDC-registered animal care facility. If you do not have a valid rabies serology titer, this must include a 28-day quarantine reservation.
Resources: