The short answer to this question would be that Fatty Liver by itself isn’t; it can’t be fatal and can’t shorten life. But the dangerous part of fatty liver is its possible complications.
If fatty liver disease isn’t treated, it could possibly lead to Hepatitis, and then to Cirrhosis. And Cirrhosis can be fatal. This is not something that happens overnight; it usually takes years, and even decades.
It is critical to treat fatty liver disease as early as possible and to not wait for the worst case scenario to happen.
I also recommend to take a liver functions blood test about every 3 month to track your progress and improvements. It’s very important to know where you’re standing at every stage of the disease.