The most urgent question facing the Emperor is what happened to Altarrin and the person who might know the most about it is the young mage-researcher he had working with him on it.
Altarrin, summoned to Jacona, was politely notified of the summons and permitted a moment to change his clothes. A stupid decision in hindsight, but not obviously one in advance; rudely dragging him directly from his work would have been running the substantial risk of annoying him, and people who make a habit of annoying important court officials don't tend to end up in positions of running important court projects. It's not that Altarrin himself would have retaliated. It's that the sort of person who would've decided to seriously irritate Altarrin would've first decided to seriously irritate someone important earlier, and so would not be present at the important mage-research site at all.
Altarrin's research assistant was not important, and so she was summoned to Jacona when two guards entered her room while she was sleeping (on opposite shifts from Altarrin, to maximize use of the headband). They compulsioned her to prompt obedience, told her to get dressed, and had her waiting for a Gate when Altarrin vanished.
Ten seconds after that they had her compulsioned thoroughly enough she could not move or think or breathe except when she lapsed into unconsciousness because of the compulsion that was preventing breathing, at which point she'd start breathing again until she regained consciousness, at which point she'd stop...
- this is not exactly the height of competence by site security but overkill is much much much much better than underkill when it comes to terrifying foreign magic, and you can't actually kill someone by compulsioning them too excessively.
About twenty minutes after that, more competent people had her set up properly for an interrogation. The first report to the Emperor comes at the half hour mark, and by the two hour mark they have most of what they've been asked to get, though obviously they'll keep it up for a week just in case there's anything they could be missing.
Most important: the civilization in the other world is real. She helped with the scrying-spell. It makes half-sense to her, she couldn't cast it unassisted, but it was a real scrying spell for routing through other planes to cross the vast distance to another world, and it worked.
Next most important is whether she's being influenced by Aroden herself, but that's much harder to answer.
Aritha Tevanir is an ordinarily, which is to say insufficiently, loyal Imperial subject; she is in favor of all the things she's supposed to be in favor of, like statistics and literacy and conquest and progress and technology, and against all the things she's supposed to be against, like the gods and the rebels and treason and the powerful order from another world. But mostly she's in favor of herself, and mostly she is wildly cynical, in part because the more cynical you are the easier it is to reconcile loyalty to the Empire with doing what is in your personal interests; it's what everyone else is doing. It's what the Empire truly is.
She hates Aroden. He's a god, and she hates gods, and he's a man, and she kind of hates those too, and if he's a story made up by Iomedae for her own purposes well she hates stories, so that's also fine. If there's mind control operative on her with respect to the civilization from the other world, it's taking a subtler form.
She believes that the civilization from the other world is going to conquer the Empire. She's loyal, which does not mean to her that she ought to try to heroically stop the civilization from the other world. That'd get her killed. It means she will obediently serve the Empire until it gets conquered which is definitely going to happen. She didn't point this out to anyone, though it showed up on her previous Thoughtsensing checks, because she figures they all knew it too; if it's obvious to her, it's presumably much more obvious to people who know things about politics. Maybe Altarrin could have figured out a way to save them, but, well, no one has told her anything about what is going on but she guesses wildly that something which is not 'Altarrin figured out a way to save them' happened.
And that does seem...useful to the civilization from the other world, so maybe they influenced her into it, though she's happy to give convincing-seeming justifications that the interrogators can't evaluate because they all turn on things like 'the magic items are really complicated in a way that suggests to Aritha incredible sophistication with magic' and 'the unfamiliar metals suggest a more advanced science of metallurgy' and 'a society that has the headbands would just have much better magical research than one that doesn't have headbands'.
Her main goal is to not get killed, and make herself useful to whoever is in power, and she is pretty much indifferent among all of the possibilities for whoever is in power including the civilization from another world. What she means by loyalty to Bastran is the same thing as what she means by loyalty to the Empire; she will serve, until someone gets hold of her head and makes her do something else, which she expects to happen eventually.
They await direction from the Emperor on in what directions they should try to scrape more out of her.