How badly have your players derailed your campaign?

Question: How badly have your players derailed your campaign?
- Keywords:
  campaign,
  spare time
Asked by anon-231599 to Felix on 14 Nov 2019.
- Felix Warren answered on 14 Nov 2019:
  
  Party split. 3 decided to run away from a invading army the other two took a bunch of soldiers and NPCs to fend off the hoard thinking “We can take them” . They couldn’t.

Question: How badly have your players derailed your campaign?