Well, sometimes encounters don't go as planned either. Last weekend the NPCs left the scene of a fight because they just wanted to go home and the players didn't stop them. The players showed up, figured they were outnumbered and let the NPCs leave with their loot (fresh beef).
One thing that I would find cool is timed events. As an NPC we always end up setting up the field and waiting for the PCs. One time we were even told "The PCs we need just started casting a ritual, so it'll be 10-15 minutes more." Well, if the PCs think their ritual is more important than saving the captain of the guard from being tortured for information, maybe they should find the dead body of the captain tied to a tree. Now the bad guys have information and can use it to their advantage.
