I was thinking, it would be cool if there was a choice when you abandon a city.

1: NPC it, like currently
2: Make it a flat
3: Make it an NPC that matches the current state of the city

It could make things interesting for farming. Would also give a good use to low level NPCs. Could capture them, level them up then abandon and keep that state, so they'd produce more resources that you or anyone around could farm. Could also make all lumber NPCs and what not.