Most corpses stay on the ground for a few seconds and then fade away, but this isn’t really happening in-universe, it’s just something the game does to prevent corpses from cluttering up the area (I assume). Things that actually have an animation for dissolving into aether are usually supernatural beings like voidsent or primals. We see and/or interact with corpses on a few occasions (especially in ARR), and there’s a graveyard near Camp Drybone where bodies are buried. Additionally, in 7.2’s MSQ…
…a human corpse did actually vanish shortly after death, and it was pointed out as strange.