Is there an ADA criteria that a successful root treatment should last "X" years?

Answer 1

UNFORTUNATELY, TEETH THAT HAVE HAD A ROOT CANAL ARE NEVER GUARANTEED ACCORDING TO ANY STANDARD FROM THE ADA.
ROOT CANALS WILL OVER TIME DRY OUT THE TOOTH AND MAKE IT BRITTLE. FOR THIS REASON A CROWN FOR THE TOOTH IS ALWAYS RECOMMENDED.
EXPERIENCE HAS SHOWN THAT A PROPERLY ROOT-CANAL-ED AND CROWNED TOOTH CAN LAST FOR MANY YEARS.

Answer 2

Dr. A speaks the truth. A root canal is an attempt to save a compromised tooth. Some of them fail through no fault of either the dentist or the patient.

It's always better to try and preserve your teeth whenever possible.