Common theme in Fantasy. First occurrence I know of in game was the SSI Gold Box D&D Game for the PC Pools of Darkness in 1992, where the PCs had to adventure through the Dead Body of the God Moander from the Forgotten Realms.

In Fantasy Literature, the first occurrence of this I remember is I believe either Michael Moorcock's Elric Novel Sailor on the Sea of Fate or The Vanishing Tower (I think it's the Vanishing tower)

Further, in D&D, the Githyanki dwell in the Astral sea, often on the bodies of Long Dead Gods:

Dwelling in the timeless Astral Plane, the Githyanki inhabit numerous fortresses constructed from materials imported to the Astral Plane as well as cities built atop god-isles, the vast stone corpses of deceased gods. Their capital and largest city, Tu'narath, is built on the god-isle of a deceased power known only as "The One in the Void."
So, lots of grist to pull from in Fantasy!