If you have unfinished River of Souls world event quests, don't abandon them! Assistant Community Manager James "Elrar" Nichols posted details in the official forums:

"It has come to our attention that the quest turn-ins were disabled for the River of Souls World Event quests. It was our intention that you be able to complete the quests if you were already on them at the time they were deactivated.

We will be re-activating the quest turn-ins soon, you can complete the quests and purchase your rewards from the World Event merchants found at:

Defiant - Boularna in the College of Planar Studies, Meridian
Guardian - Brendnall in Thontic's Row, Sanctum

We realize this has caused some confusion and appreciate you bringing the issue to our attention - thanks!"