Tooth problem. The concern is!

It all depends upon your clinical symptoms and the exact RVG (X Ray) evaluation. If you are not having any pain and still want to keep the faulty RCT treated tooth then you can go ahead with the crown and later when it gives trouble can get it extracted followed by an implant! But remember right now there's no infection or swelling but sooner or later this will Lead to infection so eventually the treatment would be extraction followed by replacement! I would suggest the earlier the right treatment the better it is! Any tooth with secondary caries if reached till the furcation ( depending upon the extent ) is difficult to save! we need to examine the patient clinically and radiographically. If your dentist is saying it can't be saved then you need to trust him because he has seen the X Ray and has examined you clinically .