Recently i came across a weird situation:
I've entered a city-like level and got message about unique on level. Lickily it was like 3 squares from the edge of my FOV, but there was Baron standing nearby. I've backed off, but when i've returned, the unique was not there. I suppose baron picked it up, but when i killed him, he didn't drop it. I am sure it wasn't blown up, as neither have i used explosive weapon nor were there acid barrels. Baron didn't shoot explosive missle.
I think this is a bug. Normally if u kill a mob which roams aroung the level and collects items, it drops them on the ground. Anyway, it doesn't seen to be that way with uniques, or hellbarons. Was it supposed to qork like that or not?