Our group made peace with the Sootscales (IMC the Rustwormer Goblins), and offered to have them mine the silver in exchange for beer. They also exacted a promise that they would not harm people.
So ... I'm thinking that the goblins will be galvanized by the PCs, and will turn the mine into a goblin city. And if the PCs take too long, I'll have them start building a road towards the PCs home.
I see my goblins like Labyrinth goblins ... but do the PCs let them move into their kingdom? If they annex the Goblin city, goblins will run amok and cause 2d6 unrest in the kingdom. If they don't, they can't have the mine. And the goblins want their BEER!
To make things more interesting, they are going to have their warriors follow the PC half-orc paladin in his ways. The PC paladin *knows* they are evil, but they will worship him and call him their hero ...