Re: root canal

Obviously, the 3 miles of dentin tubules in the tooth is if they were stacked up together (not a single long canal) - just like if you stretched open your small intestine you would have a surface area of a tennis court.
The "3 miles" of tubules in the tooth represents a tremendous area for bacteria to "hide" in. No single surgery method is able to keep the area completely sterilized (but apparently ozone therapy can be very effective though), so with time the necrotic tissue (which is a root canaled tooth since there's no blood flow) will be a harbor site for bacteria to breed in. Since there's no blood flow your immune system is not able to fight the infection in the tooth; also, since there's no blood flow, the necrotic tissue has no oxygen flow and this favors anaerobic bacteria to propagate, and their waste materials are often very agressive toxins on your system.
The rate of this progression of events is largely dependent on the dentist's qualifications and lifestyle of the patient, but I strongly think that this will occur.
Now, as far as progression to chronic diseases this depends on how well your immune system can ward off infection - your immune system will have to fight this infection 24/7 (as bacteria and their toxins start leaking into your system due to tooth and sealant decay) so if you catch a cold for example, it can take a big toll on your already weak immune system.
The fact is, leaving dead tissue in your mouth (root canaled tooth) will be breeding grounds for bacteria to thrive and this can affect your immune system significantly.
Every case is different, but often people with root canaled teeth cant make the connection of a chronic disease they developed and their mouth (allopathic doctors dont either), so its hard to pinpoint the number of cases that show root canals are tremendously risky, (there are books out there with evidence however).

As far as options go, an emerging procedure relying on ozone is being used keep infection in check (being done in europe and parts of canada).
Ultimately, extraction can be the best solution but its something to do research on the latest technologies in dentistry.
Mike