There needs to be more enemy intelligence (in at least two senses of the word) before a lot of this can be
properly implemented.
Frexample, the 'rescue mission' mode, trapping soldiers/officials and then the enemy coming in with the primary mission to retrieve them. That's not going to work well until/unless they can avoid[1] the self-same traps and thus not become insta-prisoners in their own right, for their pains.
But some variation on how the interactions are presented would be nice. Currently, you've got "Charge!" mode, "Retreat!" mode (when the former has failed) and "Mill about!" mode (when there's no path, whether inwards or outwards, according to what they
should be doing).
When I read the title I was immediately thinking of a spontaneous "dropping of weapons" by an individual enemy who finds himself unable to advance or retreat. Then there might be a removal of said enemy from the attack-lists (or, according to how Init, in-game setting or otherwise is set, change from a Hostile to something more indicative their desired non-combatant status. Which you can have your forces honour or ignore.
As it is an individual break-level (save, possibly, for it it's a unit leader) the rest of the forces can then react accordingly. Consider it worth their while to drop their own weapons (mostly if you haven't cut down their unarmed colleague, and made them more likely to
keep on fighting, surrender, or (especially in the case of unit leaders) cut down the coward, themselves and thus squash the likelihood of others doing the same.
Submitted (and not subsequently-slaughtered!) enemies could then, indeed, feature as a bargaining chip for peace (except in such race-relations that are intrinsically at war) or goods (not just with their home nation). Or else you might have an indoctrination task to bring them into your civilisation. Submitted prisoners should be assigned shackles (or at least the already in-game 'chain', as an inventory item rather than as an assigned-to building, to help keep them passive while no longer surrounded and scared out of action by military), or else they may take the opportunity to revert to 'flee' mode as soon as they (think they) see a chance to do so, prior to full indoctrination or actual caging. (Dwarves already have the "No slavery" ethics, but I don't see why a form of slavery might not be possible by such captured/not-yet-turned prisoners, in chains. Hauling jobs (not weapons?) only, perhaps. Or perhaps pump-working/workshop work with the inventoried chain
literally tying them to the building concerned.
Or so my own thoughts were, upon reading the thread's subject.
Since my own initial thoughts, though, I've also considered extending this with a 'break' level for even chain-equipped prisoners (which I'm envisaging as being "held in both hands" in inventory, or hand and foot) so that if mistreated beyond a certain level has a chance to revert to hostile, "go Sparticus" and, now, handily have a chain in their hand(s) that they can employ as a primitive weapon against unwary guards.
[1] Not TRAPAVOID, but maybe something TRAPLEARN or TRAPNOTICE