There must be some misscommunication happening here, because what I'm talking about is abandoning mechanical ownership of a town/castle; not simply leaving the town/castle with yourself and your party. Inhabiting a settlement after destroying it is madness, the settlement would be much more of a liability than an asset. This also happens to be the case sometimes even without actually pillaging a settlement, because the town is simply too far away from any other settlements your faction owns or whatever. It is for that purpose the game sorely needs an option to pillage towns without actually conquering them.
There are multiple benefits to a system like this: It removes the necessity to do some AI calculation by there not being a change in ownership of a settlement, both for the attacking and defending factions. It would increase internal faction stability for the defending faction by not giving further incentive to a clan to switch allegience due to losing their settlements. It would also really simplify my job for the reasons previously stated in regards to more smoothly ignoring a settlement which would've been a nuisance/liability to occupy.
It also wouldn't be too hard to implement. Some very simple calculations can be done for when only AI are deciding whether to take over a settlement or not: 1) "Is this settlement too far away from most of our other settlements?" 2) "If I were to accept this settlement, would I be able to tackle the increased garrison costs I'd have to pay to properly defend it?" And some other obvious parameters.
Essentially, when an AI party successfully besieges a settlement, first the people the settlement is offered to have to decide: "Do I even want it?", if not, then more and more vassals are asked the same question, until if everyone else in the faction has said no, the decision is left to the faction leader whether the faction should pillage & abandon, or just take over the town anyways.
