The factors that determine the longevity of a root canal treated tooth are numerous

To list a few,

The extend of structural damage
Heavy loss of tooth structure severely undermines efforts to save it

Your bite load
If the tooth that has been root treated receives heavy forces from chewing, this may lead to fracture and failure, as root treated teeth become brittle over time

Variations in anatomy
Extremely curved canals, accessory canals, extra canals and calcified canals can be a significant challenge to restore

Operator experience and technique
Root canal treatment inexperienced and qualified hands undoubtedly has better long-term outcomes

The go-to person is an endodontist, a specialist in root canal treatment.

Gum health
Gums that are unhealthy can be a source of infection

Your oral hygiene practices
Good and consistent oral hygiene practices will go a long way in preserving your dentition

Crowning
This is mandatory, especially in teeth that are at the back of the mouth, like pre molars and molars, root canal treated teeth last significantly longer if they have a crown

A root canal treated tooth can last a very long time if all of the factors that govern a successful outcome are taken care of.