Yes, you should keep your natural tooth whenever it is possible. 

Are root canal treatments successful?

Yes, they are. The success rate of Endodontic treatment is 95%. This provided your Endodontist assessment of the situation and there are no cracks or deep margins of cavities that could compromise the long-term top seal of the tooth. 

If my root canal treatment failed, can it be fixed?

In many occasions, it can be fixed. The success rate drops from 95% to about 75% and the procedure is more expensive.  The Endodontist will assess the situation and will decide the best treatment option.  The Endodontist will have to conduct an investigation to ensure the treatment will have a high success chance. 

Root canal treatments fail for different reasons. Ingress of bacteria into the root canal system caused by decay or a filling breakdown can usually be fixed provided the margin is no too deep under the gum. Missed canals are also common and the Endodontist can locate these under the microscope so it can be fixed.  A vertical root fracture that extends deep into the root cannot be fixed so the tooth would have to be removed. 

I had my root canal completed but I did not get a crown on my tooth.

The aim of root canal treatment is to clean and seal the canals so no bacteria will access and cause an infection. Therefore not only it is important to provide an adequate internal root canal seal but also the filling or restoration on top is crucial. It is, for this reason, your dentist will crown the tooth after Endodontic treatment is completed. 

The crown will provide stability and strength so you can chew on hard food.  An unprotected tooth with a successful root canal treatment will fail if you chew on something hard and it cracks. Deep vertical cracks cannot be fixed so this means the tooth will have to be removed.