Safe Return -- Retorno Seguro
If, for whatever reason, you find yourself with a vehicle whose permit has expired, the Safe Return Program provides legal cover for 3 to 5 days for you to drive the vehicle out of México.
You apply at your local SAT office. It's free.
The program is explained in Spanish here.
What you will need:
The car must be present at the SAT office
Valid Driver’s License
Original import certificate
Two filled out forms that they give you at the office, saying that the car isn’t subject to any legal proceedings, and a request for the Retorno Seguro.
One set of copies of all of the above, front and back