We're just finished almost a half-year long DH campaign, and I must confess its results are... unexpected.
Now, we had two PC parties running at the same time, one of somewhat loyal Inquisitorial acolytes and one of Chaos worshippers (they started as radicals, but betrayed the Imperium at some point). The storyline evolved around the feud of a puritan inquisitor Mordecai Farlowe and his radical colleague Rhia Casmirre. Both parties started from the level 1 characters and first few sessions were spent just fooling around, failing skill checks and playing pranks on the unsuspecting Imperium. Rather in spite than thanks to their efforts, loyalists have crushed several cults... each time leaving a large mess behind. This mess was then sorted out (by converting it into a sky-high pile of corpses) by the chaos worshippers.
As the characters grew in strength, so did their challenges. With the dead of radical inquisitoir Rhia Casmirre at the hands of her traitorous acolytes (who then pledged their loyalty to the Word Bearers Legions, becoming cultists of the Word) storyline drifted to the epic event called Day of Awakening. According to proscribed texts that inquisitor Farlowe managed to uncover, at this day an enomous daemonic warhost led by several greater daemons will tear its way into real space, laying waste to an entire subsector. And so the loyalists went on a quest of stopping the Daemons, while chaos cultists were given quite the opposite task.
That was the idea, anyway. In reality, the things turned out quite different.
Chaos cultists spent half the time before the Day on a planet Hebes, trying to establish their our True & Proper Chaos Cult. Each of their gambits ended up with one of their party members doing something completely inadequte, which invariably resulted in the deaths of every one of their neophytes. The most memorable event (and a good example of their modus operandi) was the moment when their Assassin decided to pray at the altar of Slaanesh. First of all, he failed his willpower test by rolling 100. Then, his roll on the Contempt of the Warp table resulted in him being struck down. Since he already suffered from Bloodlust and Blackouts malignancies, I decided that he was possessed by a daemon of Khorne. Guess what? Assassin failed his willpower test to resist possession. So, when the dust settled, Slaaneshi temple was no more and Assassin found himself several kilometers away from the place, covered in blood from head to toe and mutated into a half-spider (yeah, he rolled the Aberration mutation).
After spending four sessions trying to curb their temper... and failing miserably each time... chaos cultists worked their way into confidence of a rather notorious Noble House, adn started to work for them. They instigated an uprising in one of the planet's hive cities and wiped out a rival noble house, then blew a spire of yet another hive city (never combine a gretchin mekanik with a vortex torpedo warhead). For a moment there I believed they started to behave like true followers of Chaos. How foolish of me. Their next task was to assist in summoning a greater daemon, so that the planet might be cleansed from the Imperial taint. But, upon learning that this daemon is a Great Unclean, chaos cultists complained they don't like the smell... and instead helped to imprison the daemon inside an arcane eldar device. Then, they dumped the device inside some irradiated ruins and left.
Suspecting their "heroics" would not make their master happy, chaso cultists hijacked a starship and went to the stars, intent on forging their own destiny (and switching to RT system). While fighting for their starship, they banished two more daemons of Nurgle, earning the Grandfather's enmity and thwarting its plan to infect the planets of subsector with Nurgle's Rot. The culmination of this party's efforts was their attempt to join the forces of a Chaos Lord in their attack on the Imperium. Now, this lord was a CSM, a proud champion of the Flawless Host. Players sent their Khorne-worshipping Guardsman to negotiate with him (well, it was an accident of a sort, but other players did nothing to prevent the encounter). Negotiations ended up with bloodshed, naturally, Guardsman being cut down by the CSM champion... but, unwilling to go down quietly, Guardsman burned a fate point, crying out for a divine intervention. I gave him one chance, saying that 88 rolled on 1d100 will bring Khorne's wrath upon the Slaanesh champion. He rolled it. I know, I still can't believe it myself. So, instead of joining the Chaos Lord, party has unleashed a warband of Khornate daemons upon his citadel. In the following mayhem, the battle spread over entire planet, effectively ending any threat of a raid on the Imperium for a long time.
So, with a huge bounty on their heads (wronged noble house), hated of Nurgle, and having pissed off Abbaddon emissary, our intrepid chaos worshippers decided to give up, fleeing into uncharted regions of the galaxy...
In the meantime, loyalists were busy weakening the incoming daemon hordes. Their inquisitor (Farlowe), misled and confused by the incoherent information the party brought to him, decided the best and quickest way to weaken the daemon army would be to divide it into smaller invasions. A callous yet effective plan. So he ordered the party to summon warp breaches on several populated planets, thus luring some of the daemons away from the main horde. The plan was mildly successful, with players' actions switching from irrational humanism to excessive cruelty. In one game, they went on unimaginable lengths to save a hive city (even sabotaged inquisitor's plan); in other case, they butchered whole villages of woodsmen who just happened to be in the vicinity.
Their next step was to gather some allies for inquisitor to combat the weakened daemonic horde. Since the party has systematically wiped out almost all possible allies I planned for them, they were forced to improvise and search for unlikely candidates. They tried dark eldar twice, both times starting negotiation attempts by going on killing spree. No need to say, the attempts failed. With great effort they unearthed a lone Grey Knight (who just happened to be in the neighborhood, hunting a particularly elusive daemon). Then, they recruited the very same daemon (a lord of change, no less). I know, I know... the Grey Knight is happily unaware of this turn of events. Their true success was the mobilization of a full Raven Guard company (a bit strange company with dark secrets of their own, but that's beside the point).
As their party (now down to two active members, others being killed in action or left to rot in asylum) prepared to return to their inquisitor, they ran into an Adepta Sororitas heretic-hunting party, looking for them for past sins. The most terrible two were the murder of a Ministorum Witch Hunter and a desecration of an Imperial Reliquary on subsector capital world. One of the party members (a part-timer, playing as a space marine) merely escaped, abandoning the inquisitor and his "mad quest" completely. The other one surrendered, intent to travel to the cardinal who ordered the hunt and recruit him to the cause (how he planned to pull that off, I don't know)... but, the rolls for the subsequent warp travel were so "great", he ended up on a critically damaged starship on the other side of the galaxy, 3.000 years in the past. Goodbye, servants of the Golden Throne...
So, by the end of campaign, the situation was as follows:
1. Inquisitor got his Raven Guard allies and a "freebee" - a lord of change who organized this whole mess in the first place.
2. Daemon hordes were somewhat dispersed throughout the subsector by loyalists... and suffered greatly at the hands of chaos cultists, who banished three of the daemonic generals back into the warp, and sabotaged the gathering of a black crusade.
3. Acolytes left standing: 0.
Now I'm thinking what to make of it. Since all acolytes managed to die (and I really tried to prevent that), Ascension is out of the question. We can push the story into the Deathwatch easily enough.... but, frankly, I fear for subsector. They managed to tear several planets apart as "mere humans". Alternatively, we can just start a new party and give them a task to sort things out... but, in this case, the forces at work will grind them to dust.
Or, I can just tell the players how things went (basing the outcome on their last actions) and be done with this particular storyline. But that's a poor ending I think. So, any ideas what would be better in this case?
Move the story into Deathwatch (SM vs. Daemons, smashing subsector apart in the process)?
Begin a new party, maybe even with Ascension-level characters?
Or really just give it a rest? 
