Not leaving the game, but quitting and deleting a farmer, I usually try to screenshot the farm and/or other locations looking their best (Usually something I've been doing as I go anyhow, but the last one I try really hard to have as an "everything in full bloom and full decor" thing, not just a way to look at what's done and needs doing. I regret strongly not doing this with my first farmer ever. With Jules, her big farewell post-perfection was the spring Flower dance, so I saved images of the villagers she was talking to at the dance, and her outfits, and shinies. With Satsuki, I think I only took screenshots of the farm and house, and lose-ups on her, but with her I more petered out quietly, already planning my next farmer, and I don't think I had an official final festival.
I don't think I'm going to stop playing entirely anytime soon, though. I'm running two farmers now as is (plus one in Coral Island), and have concrete plans for the next *3* concepts.