If you haven't heard of it before, also check out Goal-Oriented Action Programming. I was looking at that for giving NPCs essentially their own questlines. So you have some random event happen ("Grug the orc steals Marf the orc's prized club!") and that would generate a quest for Marf to find his club. So he investigates; he sniffs the air (orcs have good noses). He strolls around and interviews the other orcs he sees and asks them if they've seen his prized club. Eventually, he might find his way to Grug the orc and they have a confrontation. Now, all of this is while you're sneaking through the orc hideout to retrieve some MacGuffin...