nir + udaya simply seemed correct, given this common reading of the term, but see below. I had understood vaya to mean 'cessation', as in the compound udaya-vaya-nupassana-nana - here, I understood udaya-vaya- 'arising-ceasing-', as opposed terms. This is why 'cessation' as a translation of nirodha feels inadequate to me, and I prefer the literalism of making sure a translation reflects the structure 'ni(r) + ...'. (As an aside, as I understood it, 'ni(r)' has provided the 'r', making 'rodha' unlikely.) As to 'appeasement', the word for this in Pali, I had thought, was santhanaṃ.