“Elia’s Quest” – “The Showdown” [Campaign 3, Mission 5]

Probably a bug. Due to the mechanics, the scripts shouldn't have been disrupted in the next mission. Did Horncrest come under your command? Then the heroes should have joined you. If you have Horncrest and the task is to capture Tor Thrall, but the heroes haven't appeared, you can try to complete the task with what you have :). If not, try starting this mission, or even the fourth one, from the beginning. What version of the game are you using? Is it a licensed copy?