During Bilby's quest, I accidentally put my cloak on the ground directly before death instead of using a charge of invis. When I respawned the cloak was gone. I clearly saw it laying on the ground before I died.
I forgot the name of the cloak but it was +1 armor +2 hide with some invis charges. Pretty nice cloak to have vanish for no reason =/
When items are left in Bilbys without a player present they're permanently deleted. When the quest was first opened I recall dying and losing every one of my possessions. But I believe they fixed that to an extent to where backpacks and corpses are safe - though stray litter on the ground is automatically wiped.
Ah....well damn....that really sucks.