I just finished reading Doctor Bloodmoney by Philip K. Dick. I can't help thinking that the perfect ending of the book is in the lines that come two pages before the actual ending of the novel. Once things are mostly solved, but still fairly open ended, Bonny Keller decides to escape with her lover to the city (San Francisco). Before that, most of the characters have lived in a placid countryside community, far away from large populations in a world recovering from a third world war.
"You're very good people, Bonny thought. So this is the city - this is what we've been hiding from, throughout these years. We heard the awful stories, that it was only ruins with predators creeping about, derelicts and opportunists and nappers, the dregs of what it had once been... and we had fled from that, too, before the war. We had already become too afraid to live here.
As they entered the kitchen she heard Stuart McConchie saying to Dean Hardy, '... and besides playing the nose-flute this rat-' He broke off, seeing her. 'An anecdote about life here,' he apologized. 'It might shock you. It has to do with a brilliant animal, and many people find them unpleasant.'
'Tell me about it,' Bonny said. 'Tell me about the rat who plays the nose-flute.'"
When you're doing something as open ended as writing, or shooting... when do you know that you're done and it's about time to put it all away and start something new?