jmc

We know that magnitudes of complex numbers are multiplicative: the magnitude of $|ab|$ is the product $|a|\cdot |b|$. Thus, $$\left|{\left(1-i\right)}^8\right|={\left|1-i\right|}^8$$The magnitude of $1-i$ is $\sqrt{1^2+(-1{)}^2}=\sqrt{2}$; thus our answer is ${\left(\sqrt{2}\right)}^8=\boxed{16}$. Ringo didn't give much of a reprieve.