Some more thoughts: NPC migration
As mentioned previously, loss of food supply (or housing for that matter) should give NPCs some motive to travel somewhere they believe is having fewer troubles, as well as increase their likelihood of 'deviant' skill development. When basic sustenance and safety are threatened, it just won't bring out the best in people.
However, there're other legitimate triggers for NPCs to make drastic life changes. Higher up on Maslow's Heirarchy of Needs, there's 'Self-Actualization.' If they're doing well enough on all the basics underneath, then they might just invest any nest-egg in themselves.
If we can assume the "OCEAN" phsych build for NPCs can produce a "Career Change Risk Aversion" value for an NPC, perhaps they should periodically check it against the opportunity to switch careers based on their skill sets, or skill aptitudes & training availability. If [perceived probability of success] x [potential gain in income] + cash on hand > [career change risk aversion], then they just might make a drastic life choice if they find their current station in life unfulfilling.
In a disaster, unfortunates on the low end of the socioeconomic scale aren't blessed with the most reliable information about what opportunities really lie where. Migration vector may as well just be random.
But if cities, institutions, and realms have Reputations as do their inhabitants, then perhaps that's partially manifested by a distance value--and NPCs would take that into account when they make these big life decisions. A famously successful and bountiful realm ought to be an intentional target for the economically displaced. A skilled craftsman may hear of better wages in a city down the road, and take the leap of faith even though his survival isn't threatened by staying put. The same equation may even tie into a rogue's decision to stay in town or move on---depending on how much 'heat' is on him. And NPCs stay automatically responsive to the technological advances of their evolving economies.
Once again, I don't think it has to require too much computation to make this happen.
Aim high, esteemed developers! Assure me of enough happy specifics on NPC sophistication, and I'll finally shell out some $Dough$ for you.
(I'll spare you my ontology on NPC reactivity to 5 senses & object sensory profiles. Maybe for the sequel?)