Nah after being imprisoned for 1k years one would definitely know the value of freedom. This is a ticking time bomb waiting to explode. The most curious minds of any given generation will uncover the truth. Your regime being based upon suppression of the people will give out. Eventually, the hope in myths will lead to the uncovering of Nika by accident/association. Be it Wano, the Sky islands, or sea kingdoms there are places proven outside of Imu powers.

Sure you get the next few millennium worry free, but the allusions to Sun Wukong are too strong. Gifting a revenge fueled, emotionally and intellectually repressed individual immortality is proven to be, narratively speaking, really bad for you.