Dear fellow-masters,
I was thinking about building a campaign inspired by the novel from Kipling "the man who would be king" (perfectly adapted in a film with Sean Connert and Michael Caine by the way).
Here are my first thoughts:
The PCs are part of a small contingent sent to a recently discovered planet with archaic human population. The initial plan was to absorb the planet into the Imperium and prospect interesting resources. For a reason or another (accident while in orbit or during the landing, an ambush from an enemy while the ship is in orbit, etc...) the vast majority of the personnel of the mission dies except PCs. The PCs suddenly find themselves on the surface of the harsh planet with very few resources (plus several dozens of la guns).
In the first part of the campaign, the PCs would have to gather what they can from the carcass of their crashed ship if they want to survive (foodstuff, medicine, shelters). The PCs would later have to join the nearest village of locals. With their Imperial technology, they could be hired as mercenaries by the ruling class in the vicinity and later try to overthrow these latter. They could soon forge themselves an army to carve their empire on the planet.
The end of the campagin would be when the Imperium sends a new mission on the planet. The PCs would have to face the questions of the persons in charge of the second mission. They would be rewarded if they have done well, having contributed to quickly absorb this planet and its human population within the Imperium. One of the PCs would have prepared the priests to adapt their religion within the Imperial creed. They could also be severely punished (and quickly executed) should they have during the campaign totally forgotten the Imperium and decided to proclaim themselves rulers or even worse gods among the locals.
Sorry for the multiple mistakes above. I am French.
Please do not hesitate to add your ideas.