Ideally it is always nice to have an X-ray, from what you're describing, it does sound like teeth need to be extracted. The teeth are weak from the root canals, you then had posts placed which weaken the teeth even more. When it breaks to the gum line, can be difficult to restore, there is a procedure called crown lengthening when bone is removed around the teeth to allow for me healthy tooth structure to work with. However , in your case, sounds like implants would be the best long term solution.
I'm sorry to hear about your problem. Since you say that the underlying teeth had root canal previously, it is important to have careful xrays taken to ascertain their restorability . Under experienced dentistry, it is often possible to clean out any decay, place or even replace posts and either retro-fit the old bridge or fabricate a new one to fit the restored abutment teeth. However, if the diagnosis is that one or both are unrestorable , options for fixed replacement only includes dental implants or a new longer fixed replacement. Based on bone condition, costs and the status of the potential new abutment teeth, you and your dentist should decide what is best for you. If you are having any doubts, then seek a second opinion and bring xrays, or have them taken when you get to the new office.