A spell/ritual/miracle called Sunder Spirit would be good. Obviously this could be a Darkness tool from Aysle.
It could also be an Orrorshan ritual designed to help Uthorion out since the war is still early enough that the High Lords aren’t yet stabbing each other in the back (plot twist is that it does help Uthorion now but could screw him over later).
Or maybe a desperate dark cyberwitch coven decides that if they absorb Ardinay’s soul then they could operate better within the Cyberpapacy.
Or a technodemon has been recruited by Uthorion to perform the ritual in exchange for a “permanent” Aysle/Tharkold mixed zone where the technodemon can rule over it and enjoy the high magic. The technodemon may be short-sighted in this arrangement.
Thrakmoss wants to use Ardinay’s body to fuse the avatar of Rec Stalek with a high-magic vessel. Thrakmoss doesn’t understand how magic works, but he thinks it’s a worthwhile gamble.
Dr. Mobius just wants to mummify Ardinay because that's hilarious.
Something this major likely requires some really unique components, and this can be how the Storm Knights follow the trail. First they investigate crime scenes where these strange artifacts were stolen. With proper research, the SKs discover what the ritual is and get a clue to where the thieves will strike next. Maybe they get there too late. Maybe they stop the theft, but the cabal continues with the ritual. Maybe it won’t sunder her spirit, but it could do nasty things. In any case, it probably involves killing innocents as some sympathetic ritual, so the SKs would want to stop that regardless.
Back in the D&D days, I had a story item called the Oubliette. Since D&D had resurrection so readily available, including the means of resurrecting someone without a body, I figured that the underworld had a way of keeping high-profile targets from getting resurrected. The Oubliette was an underground chamber where the victim was shackled with all their limbs hacked off but one. The remaining arm had a ring of sustenance on the finger—which kept the person alive without needing food or water. So the really high-profile targets that crossed the underworld in a major way would never get killed. They would just be locked up and immune to resurrection. Of course, there were other tools like scrying and what not, so even that wasn’t foolproof. Whether you want to pursue something that macabre with Ardinay is up to you. That’s more Tharkold or Orrorsh than Aysle, but Aysle darkness can get pretty nasty.