It depends on how severe it is, so it's impossible to give a general answer to the question.
the liver's conversion of waste products (liver encephalopathy),
death if untreated.
Untreated it leads to death.
You will become sterile if PID goes untreated; worst case scenario is death.
Hepatitis is a medical condition defined by the inflammation of the liver and characterized by the presence of inflammatory cellsin the tissue of the organ. ¨Hepatitis may occur with limited or no symptoms, but often leads to jaundice, anorexia (poor appetite) and malaise. Hepatitis is acute when it lasts less than six months and chronic when it persists longerHepatic encephalopathy (also known as portosystemic encephalopathy) is the occurrence of confusion, altered level of consciousness, andcoma as a result of liver failure. In the advanced stages it is called hepatic coma or coma hepaticum. It may ultimately lead to death.
stroke
Hypoparathyroidism
It can last from a few hours to a few days - and, in severe untreated cases, for weeks (and death may ensue if untreated).
Because - in order to diagnose the condition - you need to dissect the brain after death.
Chlamydia does not cause death or heart problems. Untreated syphilis can do so.
Diseases are "degenerative" in natuture and when left untreated, they damage the body. In the extreme even simple diseases left untreated can cause death.
NMS is considered a medical emergency since 25% of untreated cases result in death.