The NPCs in Varica are divided into two sets: playable and non-playable. The non-playable NPCs are there provide reasons for player activity. They are antagonists, trading partners, and story hooks. They actively pursue their own agendas.
Playable NPCs focus on internal development, but at a slower rate than active PC nations. If they have been formerly played by someone, then I will continue to play them along these lines. For example, the Nimosans focus on developing trade links, the Dolu purely on internal growth, and the Oerdan are independent minded and attempt to move themselves out of the Varican sphere and into a thune one.
That being said, there are usually only 2-3 'hyper-active' NPCs at a time, providing key antagonists during the game. Examples are the Sunta and Manische in the current version of Varica. Other NPCs are 'active', meaning that they are doing more than just quietly banking and developing their economies. The Romadi before they had a player, Tessil, Teraldur, Tikeecee and Five Claw are current example. As the game needs it, other players become active. With the introduction of a Nakar and a Romadi player, the Gamars and Darian March are now 'active'.
When someone says to NPC them for a turn, I attempt to follow a domestic policy similar to what they already carried out, but without any offensive moves.