Thinking some more about Thorek and his request about Karaz Ghumzul, Mathilde is in an interesting position to approach them.
For one thing, she's technically an Imperial Dwarf, just like them
More seriously, she's been a key part of reclaiming two Karaks, including one stolen by daemons and pulled into the Aethyr. Whatever caused the abandonment of Karaz Ghumzul, it's unlikely to be as bad as that. That's looking on the bright side though. Being less optimistic, in a worst case scenario, Karaz Ghumzul was abandoned by a dwarf polity that had been spared the losses of the War of Vengeance and the worst of the Time of Woe so had retained significantly more knowledge of the runecraft of the Golden Age, and had the support of the Archmages of Laurelorn. Any threat they couldn't deal with is one we're very unlikely to be able to.
Either way, depending on how the dwarves of Middenheim have prospered since they allied with the Teutognens nearly three thousand years ago, they may have built up enough surplus population to make a go of recovering their old home now that reclaiming dwarf holds has had a proof of concept. They've had a long, long time of relative peace and security compared to most dwarven settlements. If I recall correctly Middenheim has never fallen or been sacked unlike many Imperial cities, and the Underempire's connection there is relatively recent and at the end of a limb. From the descriptions, the dwarves have mainly focused on being engineers and crafting in general, while retaining the martial capacity to fight the skaven beneath the city (with human support, I think), meaning that they should have taken disproportionately few casualties even compared to other imperial dwarves, and certainly compared to the Karaz Ankor. They'd also presumably have been living relatively happy, prosperous lives and so not been so reluctant to bring more dwarves into an unkind world.
As an aside, it's hard to know from the histories we have, but if Ashes of Middenheim is roughly accurate, I wonder if the Thane of Grungni's Tower took an initial approach similar to Belegar's, allowing humans to settle the unwanted bit of his hold (in this case the roof) in return for being meat shields. Subsequently, as the humans grew in strength and the dwarves' dependence on them grew, the relationship may have shifted. If the Teutognens did originally start out as dwarven vassals/guests, you could see why that would fall out of their legendary histories of the founding of their capital - and the Karaz Ankor's information may reflect what they learned from the Empire.
However the history went, the dwarves of Middenheim/Grungni's Tower have clearly grown used to living and working alongside humans, and of using them for protection. They're also quite possibly astonishingly wealthy, sitting on top of the proceeds of almost three thousand years of trade and the gold mines beneath them. If Karaz Ghumzul is going to be unsealed anyway, one potential carrot that could be offered is information about whether retaking it would be viable.
As another side thought, harking back to comments about Thorek and intrigue. His justification for taking Karaz Ghumzul's ancestral heirlooms in reparations for their 'treason' is pretty poor, isn't it? He's not a representative of the Karaz Ankor, he's one of the Runelords of Karak Azul, not the High King. What right would he have to strike out a grudge incurred by Karaz/k Ghumzul against the Karaz Ankor for renouncing it's High King's authority. He's merely the vassal of the High King's vassal. Presumably he has checked with Thorgrim that those Grudges haven't already been struck out. It would be pretty embarrassing to go to the Middenland dwarves asking for their property in recompense and being told that reparations were already given a couple of thousand years ago and why are we taking the piss by trying to collect on a repaid debt? Dwarves don't like to talk about shameful things so Thorek could easily be working on incomplete information and pushing his luck. Let's just hope that's not the case.
On the bright side, if there are intact works of Golden Age runecraft in Ghumzul, it might be an opportunity to find out whether that rune axe we found uses utility runes.
