Point of interest is one of the most annoying things AE’s camera does.
Go to a frame where you are happy with your POI. Create a keyframe for it. Now move to the end of the comp, and paste that keyframe. sometimes, when i’m in a panic, i create POI keyframes for every new camera position keyframe, but i’m sure i don’t need to.
However, i’m no good with expressions, (you seem fairly comfortable with them), i can’t beleive there’s no expression to control POI.
Graham