After speaking to to Archmage Tevrosh for the first time, I found Hendel at his camp. I spoke to him and he attacked me, I defeated him and then his guards, but he simply stood there dazed and nothing would progress. Jaina, Tevrosh, and Pained were already standing there when I arrived - speaking to Tevrosh, it seems as though they were supposed to show up when the fight started? Either way, i waited for several minutes but the quest wouldn’t progress - Hendel simply stood stunned on the dock. Eventually I left the area and got a “quest failed”.
After abandoning and coming back, Jaina and her group were still there. I tried again and got the same result; Hendel simply stood dazed on the dock and I could not advance the quest (speaking to Tevrosh gives me the text “Hello again [name]. I hope you don’t mind the assitance, but we couldn’t have Hendel escaping, or worse, winding up dead.”