I have a friend who was diagnosed with fatal chronic insomnia. my question is: is there any survival percentage/rate? and how long a person with fatal chronic insomnia normally lives in average?

Your friend probably suffers from familial fatal insomnia (FFI). Sporadic cases are also described, termed "sporadic fatal insomnia" (sFI), which mimic the clinical and pathologic findings of FFI, but without the presence of a genetic mutation. FFI is a rapidly fatal disease with a mean duration of 13 months. There is no specific treatment for FFI.