Not necessarily just when they spawn, but these NPCs will have actual lives they're living. They'll have reasons for being in the same city you're in. You may be in a gun shop and an NPC walks in and wants to buy a gun because he's about to venture into lawless space for the first time. This system will also generate missions for players, where an escort mission could be taken from this specific planet to protect this specific NPC as he hunts for, say, a blackbox from a ship that got destroyed. These missions will also have threads, wherein a player may choose to investigate further once this mission is complete, find out who or why this ship was destroyed. That could lead to a bounty hunting mission where you hunt down a well-known pirate in the area.
Nope, NPCs will spawn with (I imagine) a semi randomised set of attributes that is affected by the BGS. This may include missions that you mention, and the NPC is likely to disappear once your interactions in single/multi player with them are complete - local attributes in your client or instance. Your activity with them will have a small affect on the BGS.
Limited persistence? Almost certainly. Part of the background sim? No, highly doubtful as the operational overhead would be ridiculous.