eq2 quest:Gehein Conglomeration  

The above post is old, but I wanted to answer the question just in case anyone else is searching for the answer like I was. It IS possible to complete this after you've already done Shades of Drinal: Incantatory Corruption. The Gehein will no longer spawn near the wizard spire, but they do continue to spawn in the southeast corner of Obol Plains, just past the Cardin Gate (-749.01, 10.04, 242.17). You may not see any Gehein at first, but if you keep clearing out the other Harrowing Horde mobs, you will.