Won't keep you alive. The liver does multiple things - synthesizes proteins, metabolizes products to make them more useful or less harmful or easier to excrete, moves blood from the intestines to the main venous blood flow system (in the vena cava), etc. When the liver is hurt from a sudden insult (tylenol (acetaminophen) overdose, etc) or long-term exposure (alcohol, heptatitis c, etc) 1 or more of these functions can't be done.
What the name says. It is a liver no longer capable of serving its normal functions. It is treated symptomatically at first, and then, if available, with liver transplantation.