Thank you @SzethIsBadAsHell
I really think that it is really possible that Humans killed a delver, Or they came across one such corpse, then made a base on it to study it. I really think that it is possible originally a minimal population lived on the actual planet and most of the humans, scientists etc lived on the platforms surrounding the planet.
I am quite sure that we will discover some way in which delvers can be killed.
Mainly it is the tunnels and similar writing and I think the presence of nowhere portals, it is possible that a delver corpse and his delver maze might have made making nowhere portals easier or had naturally occurring portals in it.