Since the thread is dead and buried, I may as well hand out spoilers for what I had planned.
The party would end up learning that the first village they were sent to recon had been sacked and turned into an encampment for the marauders and mutants who were led by a dark eldar. The party would regroup at the listening post and plan to recon the second village and learn that the marauders/mutants are being led by a small squad of dark eldar. The party then would, with the help of the villagers of the other town, learn where the dark eldar squad is camped, attack and kill them. The marauders/mutants would flee or surrender.
The party would later piece together that dark eldar had allied with a chaos cult to raid the planet. The cult wants to rise against Imperial Rule and take over, but the but when they learn the dark eldar only want to raid, take prisoners and then leave, their alliance breaks down as the Imperial Forces rally and crush the resistance and comes to the rescue.
Once we got off the island with the help of the villagers we had saved, we would make our way back to friendly lines and the adventure would pretty much be over.