i've died multiple times from falling a long distance but a couple times i've been unable to retrieve SOME of my items. i've died from falling and immediately went to get my stuff (took no longer than 20 seconds so i know it didnt naturally despawn) but the only items i had left were my armor. 

tldr: i fell from a high distance, went to get my stuff in less than 1 minute, and the only items that appeared were my armor.