The group splitting up. My idea with this was characters splitting in a dungeon, not players leaving the game. Sorry for the confusion there.
How do you use good monsters in your campaign? In this sense, I meant how to you employ mosnters in other ways other than combar--I know with good monsters (creatures from the Monster Manuals, whatever you want to call them), they can be used as NPCs or as bargainers between the players and themselves. I was just wondering how you personally implemented these non-combat monsters into your campaign. However, regardless of the confusion on this, the answers were still interesting.
Thank you so much especially on all your advice on "taking a 20!"