I slapped on my Boots of the Bay and nuked some bloodsail pirates. By using mana shield (expires after 1 minute) as a timer, I observed the following:
- looted immediately, despawned after 3rd cast (2 minutes)
- looted after 1 minute, despawned after 4rd cast (3 minutes - 2 minutes after looting)
- uninspected, despawned after 6th cast (5 minutes)
- inspected, despawned after 5.2 minutes (5 minutes after inspection)
- inspecting each minute, lasted 10 casts (did not wait for despawn) - mob did respawn at 8.4 minutes. Killed the second mob, looted and the new corpse despawned after 2 minutes while original corpse still there.
- killed and looted a jaguero stalker (skinnable). The corpse despawned 5 minutes after looting.
So, it seems that 2 minutes is the despawn time for looted corpses (unless salvagable, then it's 5 minutes). If there's loot it will despawn after 5 minutes. Inspecting the loot resets the timer.
It makes me wonder if that corpse remained there because
The neighboring corpses were looted and despawned after 2 minutes. This corpse stuck around for 3 more minutes with its loot, or you inadvertently inspected without looting causing it to remain for an additional 5 minutes.
I also scoured the patch notes, and the only one mentioning corpse despawning was for 2.4.2
Looting a boss while a player is outside of the instance will no longer cause the corpse to despawn in 2 minutes if the player still has loot on the corpse.