How tempered were/are the Gnath/Vath?

[Iscah]

Part of the tempering, when you cure it, you have to remove the memories of it.
The hivemind will ALWAYS remember being tempered.
They are the only beast tribe that can never be cured... not unless you killed every single member of the species until it was only the eggs, and then wiped everything from THEM all at once.

Or maybe a single fertilized queen.

That depends entirely on where the tempered memories are stored and how "polluting" they are. The lorebook indicates that there is one central Gnath who houses the Onemind, so perhaps curing them or even replacing them is enough to fix the entire colony.