Just let them go.
Actually, be extra nice to them and give them a long corridor especially for the purpose with something that goblins especially love, such as *serrated green glass discs*.
Anyway.
A minotaur showed up. He did not have an invitation to Roughshaft so I didn't bother lowering the drawbridge. He also refused to enter any of the guest palanquins (i.e. cage traps). I decided to let him wander about a while in case he'd get bored and wander off. Of course that's not happening.
Later the liaison and the annual caravan from homelands show up. The liaison runs into a band of goblin experimental medicine students (bowmen) but does not survive the long-distance acupuncture. On the other edge the merchants run into another band. The merchants try to flee, and the lonely minotaur rushes in to help, giving the goblins a lesson about civil manners and some friendly patting with his maul. Caravan guards join in as well. In the end only the guards are standing.
This is too much for the merchants. One by one they lose their minds and go berserk. Goblins help one to calm down permanently. Two others have a spirited discussion and only one survives. The remaining merchant stands still, fuming in rage. Caravan guards have no caravan to guard any more so they depart.
Elsewhere, the militia of Roughshaft emerges and meets a band of swordgoblins. They don't have an invitation either, so they are requested to leave. They do so, so swiftly that a few of them die of whiplash.
The citizens of Roughshaft proceed to claim the spoils from the battlefield. So many bloody (troll fur socks) to gather, and all the merchandise. The berserk merchant punches a hole in a bowyer's brain, so the militia make him calm down. The overseer queues up another batch of coffins.
"The Caravan from Fikud Likot is departing."
While the citizens finish up stockpiling the goods, the final survivor of the caravan, an insane merchant's yak, crawls off to the edge of map and alone takes news of the event back to Mountainhome.