The Sims game should have the option to make some members in a household NPC. Think about it.
With the option of changing a member of the household to NPC or from NPC would allow the player to focus on the story line of some individuals while then back to the others when the player is ready to...
With the Road to Fame mod, I have the option to make my celebrity Sim an NPC celebrity, but I enjoy playing him. So, I haven't taken advantage of it, yet. Nor, do I expect to ever.