Bug: The Missing Diplomat

In WoW Classic Era, the quest “The Missing Diplomat” is bugged. This is a quest chain, and I am referring specifically to the quest accepted by Hendel in Dustwallow Marsh. The quest is to kill Hendel, but according to multiple sources (many of which are old…) if Tervosh, Jaina, and Pained are present for the main fight, the quest will bug out, and the npc’s that arrive to help you just stand there until the quest fails. If you abandon the quest, it will not become available again from Archmage Tervosh. Can someone please fix this quest? It’s apparently been broken since the initial release of WoW in 2004.