Possible retreatment or extraction for a root canal? (Photos)

The best and most long-term successful solution to your problem would appear to be extraction of the infected root canal tooth and placement of a dental implant. While the upfront costs can be larger the long-term success is far greater.
If that is not an option for you, I would recommend you retreat this tooth rather than simply extract it or have partial made.  The biggest problem with the bridge would be that you would have to cut down a perfectly healthy canine tooth as well as lose bone. Often times bridges will need replacement at least once in their lifetime increasing treatment and costs.

 Re-treatment by an endodontic specialist have a much higher success rate than by general dentist.  No treatment of that tooth will have a 100% guarantee success.  An endodontist is well-trained to rule out all possible reasons for failure of the original root canal. I would recommend following through with your endodontist. Retreating and keeping that tooth is the most desirable and least expensive option. 

Thanks for the X-rays.If the endodontist feels that retreatment has a high probability of success, have him or her do it.You do not want to remove this tooth! Did they capture a cone beam 360 degree x-ray that would show if there is a fracture present in the root structure? If there is a root fracture, the tooth will need to be removed! Talk to theendodontist about the cone beam x-ray - it would rule out a fracture and thus make the decision to retreat more acceptable.