I hear from a lot of blog readers and students that they work on their journal sketches later, if they can’t finish them when they first set out to sketch.
I believe a journal needs to reflect your life.
That puts me in the “move on” camp if a page isn’t finished because I get interrupted.
So just as I had to move on from my soda pop tests (because the pop was stored for too long and went off), so I leave sketches if something interrupts me.
I think it makes for interesting pages that reflect my life.
You get to decide for yourself which camp you want to be in; and what reflects your life.