Two failed root canals being retreated...is it possible that re-infection could have resulted in an osteomyelitis of right lower jawbone?

Yes: Root canal treatment primarily fails due to 1: residual bacterial infection of incompletely treated roots, 2: re-contamination of the rc filling from decay in leaking/failed dental work or 3: trauma. Osteomyelitis is a bone infection from many sources: teeth, blood, bone fractures, residual infection (involucrum), or others. Sometimes, the source is not known-even distant to site of infection.

Maybe: Anything is possible. Infected areas can cfreate dangerous effects. This is possible, but not probable.