Originally posted by Ash:

Same here! 2 tombstones disappeared. Mistlands. Didn't have the freeze problem you describe, I just died 2x in a spot, seeker that killed me destroyed my portal. When I got back to the spot about 2-3 game days later, 2 tombstones were gone, materials of destroyed portal and workbench disappeared too.

The workbench is what prevents nearby materials from despawning. With the workbench gone, the materials will disappear at some point, though what the timer is I do not know.