Sera's quest broken - Cannot complete Crestwood part

Attempting to do Sera's quest.  We go to crestwood and get ambushed but then the NPC needed to continue the game simply does not materialize.  Reloading a save from before and going to Crestwood again does not change the outcome.  This is a major game breaking bug as it prevents any further progress since the player cannot leave the area by any means.  I had to reload an earlier save and just skip the quest.