Until he is 19, he is still under Ju-Vee rules:
As of now, the most severe punishment Couch could face is 120 days in adult jail, Tarrant County District Attorney Sharen Wilson said at a press conference
http://www.cnn.com/2015/12/29/us/affluenza-teen-ethan-couch-detained-in-mexico/
That's only for fleeing jurisdiction - not for violating probation. That's a more serious charge, if the D.A. decides to pursue it.
Oh just made it. He is now 19. His mom is in line for about 10 years. That is real justice.