The Plot Thickens

Somewhere in the bowels of the mine, the moment arrives where, with or without the assistance of the gnomes, the party succeeds in defeating the orcs and freeing the prisoners. If they are still alive, that is.
Before the last of the orcs expire, they will spit at your feet and promise retribution against you for your crimes. "We are only the first snow in a long winter, your doom awaits you in these hills. Even now, forces are approaching that will crush your bones to dust!" (They were poetic orcs, apparently).
Semantics aside, they are part of a larger operation intent on using forced labor to become rich. This tribe of orcs, led by a half-educated former adventurer named Granak Smith, has decided the key to success is not in making your own way in the world, but in following the money. They have systematically been plundering other mining transports and shipments, bolstering their coffers and their ranks. Now, they have decided that ambushing and fighting is too dangerous, and that if they just took control of the mine, they could take all of the profit from it, while forcing the former owners and miners to do the actual work.
They entire tribe appreciated the simplicity of this approach. Very quickly, they struck out taking over a small mine. This success led them to take over a larger mine, one with 30 miners throughout a five level deep mine. This was also successful, but with the larger mine and the more prisoners, they also attracted greater attention. They insist their takeover was at the request of the owners, but since they killed them before the uproar, they have no way to prove their point.
Now, they have decided to kidnap the gnomes and force them to "sell" to them, but the PCs interrupted their plan. They are watching the mine, and will get word back to the main tribe about what happened, and more importantly, who was responsible for their loss. They will hound and attack the party.
The party doesn't know any of this backstory, but once the seed of revenge has been sown, they should have ample opportunity to learn the crux of these things, or at least rumors suggestive of them, from any miner encountered in the wild or back in town.
Assuming the gnomes survive, they will request an escort back into town to meet their employees, and to secure additional security. They may be interested in hiring the PCs to fill that role, even in a temporary capacity.
Talking with townsfolk will reveal that this has happened at other times, though not in town. Travel on any of the roads is risky without lots of support. Investigation checks around town (DC18) will be able to piece the whole story together, and give the name of the suspected leader and the larger mine they have taken - The Hardy Claim.
The Hardys started the mine about 20 years ago, and after 7 or 8 lean years, struck a deep vein of gold that kept playing out, allowing them to dig deeper and deeper, hiring more and more miners. It is still a smaller sized, personal stake mine. The general consensus is that the orcs took the mine by force, the Hardys are dead, and the miners forced to work under brutal conditions. Knowing and addressing are two different kettles, however, so the orcs have been able to continue in a mostly open way. The attack on the gnomes in town has put most of the townsfolk on edge, and given them a reason to ask you to deal with the orc tribe and the Hardy Claim.
They can give you a map showing the location of the claim's main entrance. It is located on a lone peak, smaller than many of the larger ones in the main mountain ridge behind it, about 5 miles from the gnomes' mine. If the PCs are able to roll a 25 on any of their Investigation checks, they can also learn of a secondary entrance to the mine on one of the lower levels. It is on the third level of the mine, and is partially flooded from a collapse near where a small stream flows out of the hillside. This is the better method to use for a stealthy incursion.