Looking through the MQ05b quest script, when the quest starts, if either Sickle or Hammer are dead, the quest fails and the objective is turned off.
After the quest starts, it monitors for Sickle being killed. When Sickle dies, the quest should fail.
Instead of all the convoluted console commands previously mentioned, try this:
cqf SS2_Sirick_MQ05b FailQuest
This calls a quest function that should handle all the behind the scene things and turn off the objective.
To look into:
The script function turns off objective 30 on SS2_MQMaster. Need to verify that this is the correct objective ID. Its possible everything is working correctly except its turning off the wrong objective.
You should enlarge the font and bold it!
Note: Most of the SS2 magic happens via script and the source is not publicly available.