I disagree that scripted NPCs have nothing to say. You have a few basic types:

* NPCs that don’t want to speak and usually offer a dismissive comment or a single repeating phrase. Fine candidates to LLM so long as this pattern doesn’t change. But also, who really cares?

* important NPCs with specific written dialogue. Don’t even THINK about gambling with your story’s self consistency by giving these guys agency

* the limited townsfolk type that has a small bit of something say. Like a typical Baldurs gate NPC. These people are fun to talk to because they “might” have something relevant or fun to say. Usually you don’t have to say anything. They just want to share things with you. It would be very tedious to chat with these people if they were infinite wells of lore and nothingness to be probed with written language.