Well, firstly, it would have poisoned the mind and soul of the High King that sat upon it, and through them, the dwarfs.
The Rune of Azamar is of incredible importance:
Azamar, the Rune of Eternity struck into the Throne of Power, was the work of Grungni himself. The Rune of Eternity was so powerful only one of its kind had ever been wrought, and it could never be duplicated. Bound within that single rune was all the craftsmanship, all the tenacity and all the iron will of the greatest of the Ancestor Gods of the Dwarfs.
As the legends tell it, when Grungni was done with his creation, he stepped back to assess his work. He was a harsh and exacting judge, always demanding perfection, and never finding it. In Azamar, however, Grungni was wholly satisfied. Still, being thrifty in praise, Grungni made only this promise; so long as the rune of Azamar endures, the Karaz Ankor shall never fall.
So no longer having the Rune of Azamar for the dwarf people would be a bad thing, especially if they managed to get the throne back to Zharr-Naggrund and do all sorts of nasty things to it.
It wasn't a sure thing of activation, either. They needed the High King's blood to do it, and if he hadn't been caught like you all were, that would have been harder. Plus, the throne might not have been in a position to be taken, though in this case it was saved by Urgdug.
Within a year? Probably not. It would have been a slow, grinding thing as was meant to be and presumed by the dawi. Updates would have come every turn as they slowly dug their way down.
If they rolled spectacularly poorly, yes it would have been horrific. The runes protecting the Dammaz Kron would have probably kept it okay, same with the other stuff, but some damage would have occurred. At the same time, no guarantee that it would have gone super badly either. We're getting into a matter of many rolls, long ago, distant from the player's eyes, that it's difficult to speculate as to what precisely would have happened depending on the rolls. They could have rolled amazing instead, and instead of getting super granular as we ended up doing, a few rolls might have encapsulated whole floors and levels at a time outside of granular moments necessarily. High King lost would have caused massive damage to a lot of things, I'm not sure why that needs to be extrapolated on, honestly.
It's pretty obvious the consequences of losing the High King, right? Like I don't need to explain that that would be bad?
What would have happened? Lots of bad things?????