I've had my root canal several years ago and still no crown over it. if i do that, will the tooth last a life time?

No guarantees: In medicine and dentistry. We are not dealing with only a product. Even if we were, you probably notices less and less things are guaranteed and when they are, it is for shorter periods of time and with more restrictions. A dentist cannot control how you eat, how well you keep your teeth clean, how often you come in for checkups, etc. Discuss treatment and prognosis with your own dentist.

Maybe: Even with a root canal and crown you may loose your tooth before the end of your life. You will surely loose it if you don't have a crown placed as it will more than likely decay and not have enough tooth left for a crown.