Taking your age into consideration, I then tend to agree that alternative options should be considered rather than extraction. The decay I mentioned is distal of tooth number #14. The endodontist will most likely take a 3D scan to confirm restorability of both teeth.
Deep Margin Elevation is a well documented procedure for teeth with decay below the gum line, although not all practitioners have the skill to perform this. Unfortunately this means that you will have to bring this procedure up during the consultation with the endodontist, and if he is not comfortable doing it, there is a chance he can refer you to someone in the area that can.
Subgingival amalgam is also a good option, but to do a proper filling, you will need to ensure adequate marginal seal, and either crown lengthening or deep margin elevation will be required to achieve this seal.
Regrettably the endodontist yesterday did not see any alternative to extraction.
I mentioned Deep Margin Elevation to him, but he seemed unaware at first of the procedure. When I showed him a diagram, he acknowledged having seen something like it under a different description. I asked whether he knew another specialist who might help me but he demurred.
The endodontist I saw is part of a network served by the dental insurer which covers me. When I first mentioned DME, he called it a "heroic" procedure without much chance of success. It occurred to me (with no real evidence) that network dentists may not be paid enough to use procedures other than those which have been taught in dental schools for decades.
Extracting #14 and #15 is an undesirable outcome for me, but finding someone skilled in DME who would be willing to restore them is more difficult than I anticipated. Today I became aware of a supply house named Garrison Dental which hosted online webinars on DME so I called them and got a list of their customers in my county. Possibly one or more will know someone who is capable in the field.
The endodontist's report today said that I was asymptomatic upon presentation. It reminded me that I am lucky not to be in pain from #15 which lost its crown and that I may have "enough" time to locate a DME provider with the necessary skills.
Thanks again for listening.