Quest items gone, cannot progress the campaign

Cannot progress the campaign in Act 2 Cruel difficulty:

Quest 1: The trial of corruption - Recreate the Horn of the Vastiri
Quest 2: A Theft of Ivory - Pick up the Mastodon Tusks

I have lost both the quest items and have tried to kill the same bosses again but does not help. Can we Reset the quests somehow? I am now stuck in the campaign and don't know how to progress.