Well, considering how long it's been down there, and what it's made of, I'd say it's safe to assume that those orcish drillers will die of old age long before they reach wherever it is they're going.
This did get me thinking, though. One type of monster I'd love to have added to UO is the tunneling type - something a la purple worms from DnD, or the sand worms from Dune...
*you hear a rumbling noise below you, and the ground begins to shake*
Followed by something bursting out of the ground, making weird sucking noises.
*waits for all the jokes about UO already making weird sucking noises*