If i suspect a dental infection and its left untreated and it spreads is that damage reversible?

Possibly. Bone that is destroyed by a chronic infection does not miraculously regenerate to its pre-infection state. Periodontal disease results in loss of bone and gingival attachment. Often trying to rebuild bone and lost teeth costs way more than treating the problem in its infancy.

Many articles over the last 10 years in well refereed journals linking gum disease to brain damage, especially stroke, cardiac damage especially heart attack, kidney/liver/pancreas/urinary tract damage, short term pregnancies, and the list goes on. All infections cary with them the chance of permanent damage to the infected organ system and, via the circulatory system, other organs.