SRD "declined to commit" as to whether or not the Elohim who became the Colossus of the Fall could escape her Appointment after it had become moot (because the Sunbane destroyed the Old Forests whom she had been Appointed to save). Seems to me he is leaving the way open for Findail to escape his Appointment, if something happens to the Staff of Law.I think, taken as a whole, what we learn about all the Elohim is they are all creatures of ego.
And the loss of ego would be the most unimagineable horror possible.
They are too egotistical to withstand being made part of the Staff of Law.
My opinion, anyway.
Vain was "pure structure" and not a living being; but Findail is a sentient, living, and personal being. I would say that Findail has unfinished business with Kastenessen, and there is the possibility that there will be more with them-- even if it means Findail as Staff of Law.