How dangerous is wilson's disease?

Extremely. True Wilson's is fatal if neglected, and it is an especially gruesome way to die, with progressive brain damage compounding liver failure.
Prognosis of WD. The prognosis in patients with wilson disease is excellent for most. The neurologic, psychiatric, and liver abnormalities gradually improve with treatment. Poorer outcomes are seen in those with advanced disease and those who present with rapidly progressive liver failure and breakdown of red blood cells (hemolysis).