failed root canal tooth extraction?

My boyfriend who is almost 28 has had a lot of dental problems due to not having dental insurance for a really long time and not taking care of his teeth when he was younger. His job doesn't offer dental insurance so he bought a plan offered in our state which is decent and at least covers some stuff. Last October he underwent two root canals and that was that. They were causing him a lot of pain at the time but after the root canal things were fine. Cut to this week he had an appointment with an oral surgeon to have his wisdom teeth pulled. They x-rayed his teeth and told him that one of the teeth he had a root canal on ( #19) was really really infected, to the point where they weren't sure if it could be saved. He's lost quite a bit of bone according to the xray. We postponed the wisdom teeth removal, went back to the general dentist and he referred us back to the dentist who preformed the root canal. She said after doing a test of the gums around the tooth (which she said involved poking the gums and if one side goes really deep that means the tooth is cracked) that the tooth is cracked in the middle and not salvageable.

Obviously this was seriously upsetting news after the all the money dumped into the root canal and crown not to mention the potential cost of an implant and not having a molar on one side of the mouth for awhile. We asked the insurance for a second opinion but in the mean time my question, is there any way she's wrong about this? She was very certain that the tooth couldn't be saved, but i just don't see how it's that simple and there isn't a possibility that once they open the tooth that it could be saved.