Ant Hill Ease
Ultimately, Inarra lets Tump take the lead since this is technically not her descent. Her main purpose was to get the two of you motivated.
After Django describes the location where the explosion blocked the halls and where he ascended being chased by the serrataraptors, Tump is able to triangulate a couple of possible routes. Looking at the known areas of the enormous building, what used to be the top floors, it appears that the Voidchasers should have made it out already. It leaves only one conclusion...
...something has happened to them.
About two hours into the search, there is kind of an explanation. The scenes of a recent battle against a mid-sized denizen are evident in a larger arboretum. The sanctuary is out on a terrace that would have been out in the open air and sun in ancient times. Now it hangs in darkness out over a 6km drop to almost certain death.
In the center of the arboretum is a vast hole, large enough to drive a transport truck through. However, it's not just an empty drop. It looks like some thought went into the explosions that cause it because only three sides of the platform detached. The fourth remains intact, though it twisted the back portion of the platform up. The missing floor forms a ramp down to a narrow balcony four floors below. A door is missing, blown inward. There are no bodies.
The most concerning thing is, whatever they were fighting, it would have been too big to go through that door and might still be around, hiding.