Soooo, I was in the wastelands attempting to solo Momentus (eventually got him) and ended up losing everything I had on me because it was gone when I finally managed to kill him. I found this especially irritating as Momentus got stuck in a water hole right on top of my stuff so I couldn't even lure him away to get it back. Is it normal for this stuff to despawn? I though our items remained indefinitely if they dropped when we died. Normally this wouldn't bother me but I lost a lot of high end gear 1 silk touch diamond pickaxe 1 fortune 3 diamond pickaxe 1 Eff 4 diamond pickaxe Diamond armor +tons of mined iron, gold, coal, diamond and other loot.
I think they despawn in 15 minutes. If they would not, their would be way too many items laying on the ground from players who didn't care to pick them up, and it would lag the server.
I believe that in vanilla MC your items take 5 minutes to de-spawn if the chunk is loaded, however if it's not the items will remain indefinitely. As for EMC's timer, it could have been extended to 15 minutes.
I quoted patch notes from Aikar on the disposition of the despawn timer in EMC. Yes, the despawn on VMC is 5 minutes, but Aikar has coded Empire to have a 15 minute despawn. However, as I pointed out above also, the items could have been pilfered by enraged spawn, unless pickup has been disabled for hostile mobs. However also with my experiences with the minibosses, the items could have been glitched into the ground or something. I have also noticed that when items are dropped upon death and picked back up and the player again dies, it seems as though the despawn timer does not reset for those items and you have less time to pick them up if they don't completely disappear with the second drop..
You should post it here to get help http://empireminecraft.com/threads/server-problems-post-here.35765/
Since Momentus doesn't despawn, he may have kept the chunk loaded long enough to cause your items to despawn without you being there..