Tooth # 15. Or should I seek another opinion.
Without an x-ray, it is difficult to confirm or deny a treatment plan. However, normally, if a tooth has extensive decay that extends below the level of the bone, the tooth may not be salvageable. Even if the decay is removed and the tooth receives root canal therapy, a post, core, and crown, there still has to be enough remaining tooth structure above the bone level to support the crown... especially in the molar/posterior region, which experiences strong chewing forces. If a post, core, and crown is placed on a tooth with insufficient structure above the bone level, the crown is very likely to break off during normal activity. However, if the tooth does in fact have sufficient support for a root canal, post, core and crown, then its better to have a healthy, supported natural tooth.It is always valuable to have a second opinion, but if the tooth does need to be extracted, look into a replacement for the tooth, like an implant or a bridge, so that your chewing and bite plane is not compromised in the future. Good luck!
A tooth that has been damaged by decay may be too far gone. A qualified dentist you trust, that is involved in all aspects of dentistry should evaluate the situation. If the tooth has a good prognosis then saving it is a great idea, the tooth may need crown lengthening surgery or orthodontic extrusion to make the crown more stable, its not a good idea to have the crown supported ONLY by a post.If all of the above wont work then your best bet is extracting and replacing it with an implant. Now-a-days we have Ceramic Implants that mimic the function, aesthetics and health of natural teeth.In terms of the life span of the solutions, a crown/post combo will likely give you 5-12 years. An implant taken care of likely 15+.Take care.