Grusha's Whereabouts

"I seek, with mortal desperation, the final gift of Giath, that brings one's deepest desires into being... the Black Stone NPC Knowledge Item..." - Grusha NPC Knowledge's note -

A note filled with bitterness and resentment toward the world, found in the streets of Heidel one day. It was written in Goblin tongue and clearly Grusha NPC Knowledge's handwriting. A search party was sent out to find Grusha a day that turned into two days... then into a week. Where could he have disappeared to?