Honestly, I would be fine if I was able to drop a mission because I faied it x# of times or something like that. Maybe once you reach #### worth of debt (sliding scale of course) from one mission, you are able to choose to delete or fail that mission.
In addition to that would be the ability to drop older missions, say if a mission now has nothing but greys and greens in it to you, you can drop.
It's not about convenience as much as it is about not wanting to reach 10K debt just because the Sea Witch (@ level 24) just won't drop dead at the sight of you like a good little girl.
