[x] THEORY: The specifics are hazy, but this is a known contingency plan that Borek is entirely aware of, but hoped hadn't been enacted. The result breaks all Dawi notions of acceptability, but Karak Dum survives in some capacity and continues to inflict attrition on every local and visiting Chaos force that want to take a swing at them, so it is considered a lesser evil by the pragmatic Karak Dum.
[X] THEORY: The dwarves of Karag Dum are alive and uncorrupted by Chaos, but have resorted to truly drastic measures to survive, probably undertaken by their controversial "Rune Masters", which involves having these beastmen or beastmen-appearing creatures defending the karak for the dwarves. We can assume that this is all in favour of the dwarves by Morghur's easy acceptance and non-destruction of Borek as well as Borek's mutual acceptance of the beastman. The idea of Rune Masters being critically involved is the certainty that some form of magic was used to create this whole situation, including the odd weather, and the Rune Masters' lack of corruption is supported by the lesser level of ambient dark magic in the area, even directly around Morghur himself.
[X] ACTION: We need to verify if the situation here is stable, or if it's something that will come back to haunt the Karaz Ankor and Empire if left ignored.
[x] THEORY: That's not Morghur. Morghur constantly changes his surroundings, Morghur does not make reality more stable near himself, Morghur does not display affection, Morghur would never stay here unless he was bound, and if he was bound he'd be struggling constantly to get out. The shuddering of reality can be faked by Runesmiths if they wanted.
[X] THEORY: Through either Pact, Binding or some other venue the dwarfs of Karag Dum have installed Morghur as some form of defensive guardian, supported by the fact that Morghur is treating the mountain as a giant herdstone while to my vision it is not. The confounding factor here is that the energy flowing out of Karag Dum is uncorrupted. Morghur himself would almost certainly be using it for his own ends, so it means the occupants of the hold either don't know how to use it, don't care to use it or still consider themselves part of the Karaz Ankor enough that they let the energy flow uninterrupted.
[X] THEORY: This could be a Rune-based Illusion with "Morghur" being a Runemaster. The Dawi of Karag Dum let the forces of Chaos assume that Dum has fallen and is surrounded by Beastmen forces so they don't all unite to attack the Hold together and instead only come in smaller groups to "test" themselves against another chaotic force.
[X] THEORY: The Dwarves of Karag Dum did something to burn away the taint of Chaos, much as your Belt of the Unshackled Mountain does, but on a far grander scale. Perhaps it had an effect on the Beastmen here, Cor-Dum included.
[X] ACTION: The forces should move back at least a half-days distance, find a defensible spot, and camp out for a few days to give them a chance to investigate, but no more than two-three days, the overall safety of the expedition still comes first.
[X] THEORY: The Dwarfs have control over Cor-Dum and is likely being controlled by Karak Dum's King or Leader, They are doing this to protect Dum and keep Chaos from getting hold of it, there is an ongoing siege to break this defense with a nearby source providing power to the desert to weaken the defenders.
[x] THEORY: Morghur was reborn as a dwarf and at least partially protected by the Valayan rites, subsequently those protections were relaxed to allow him to mutate physically while retaining self-control and his dwarven identity.
[X] THEORY: That's not Morghur. Morghur constantly changes his surroundings, Morghur does not make reality more stable near himself, Morghur does not display affection, Morghur does not not attack people, Morghur would never stay here unless he was bound, and if he was bound he'd be struggling constantly to get out. The shuddering of reality can be faked by Runesmiths if they wanted.
[x] [THEORY]: There are no dwarves to save. Either the "Cor-Dum" we saw is somehow fake, in which case the dwarves hold the place, and need no help holding it; Cor-Dum is real and allied somehow with the dwarves, in which case the dwarves are not worth our trouble as they have allied with chaos; or Cor-Dum is real and conquered Karag Dum, in which case there are no dwarves left to save.
[X] THEORY: There's some sort of strange illusion magic going on, and it's not visible even to extremely good mage sight. Out of all known sources of magic only Dawi Runes are capable of that - so the works of Dawi Runesmiths are still in use.
[x] THEORY: Whatever the hell is happening, Borek seemed to still care for what Karaz Ankor thought of him and that what we are seeing is the result of his home trying their best to fufill their duties in ways the rest of dwarves probably wouldn't approve. The Corrupter seemed to recognise Borek as almost kin and hasn't made a move against us. I think some very careful investigation is warranted.
[X] [Action] Scout the other fronts, ask other expedition members for what they might have happened, check with the other wizards what their expertise tell them about the magical and natural environments.
[X] ACTION: Very careful scouting. Both by the knights, dwarves and Mathilde. Starting with inanimate matter and other disposable stuff(like the cows) to determine where the edges-borders of the effect are and just what the hell the effect is without entering it, while the convoy digs in and readies itself to attack, from behind or from the Karag. If that doesn't lead to some clarity, more aggressive scouting may be needed. Either way, Karag Dum is still a part of the Karak Ankor, and there are ways that link them could be used by demons to hurt the whole realm, especially now that Vlag is back and the links reestablished. So while a part of me might prefer as the wise option to turn back, we cannot leave such a threat without establishing its exact nature, if only so I can bring back news of what to do to about it to King Belegar and the High King.
[X] ACTION: We need information. The Yusak have been in this area for long enough, they must know something of what happened. The wagons will pull back to their territory, and while they are en-route I will attempt to directly ask Morghur (From a distance, using a spell) what has become of Karag Dum. If the worst comes to worst we will already be retreating and I will be fast enough to catch up. We will figure out our further course of action once we know more.
[X] ACTION: Mathilde will infiltrate the hold and look for more answers. In the mean time the convoy should circle the Steam-Wagons and avoid provoking a fight they can't win. If she has not returned within 24 hours they should turn back and attempt to make their way back to civilisation to inform the Karaz Ankor, Empire and Kislev what they found.
[X] THEORY: Neither Morghur nor beastmen are what they appear to be - they are instead dwarfs of Karag Dum, who changed bodies through principles they knew but still kept their souls and minds intact. The reason for that was the need for new bodies that could survive fighting in the Wastes. "Morghur" is a member of the Royal Clan or a Runemaster that knew Borek personally, which why he made such an intimate gesture. It is possible that not all dwarfs suffered such fate, if that is the fate they suffered. Borek knew of such plan, but found it shameful and thus fell into despair when he saw it done.