... it would mean that we wouldn't do missions into that sort of fanfic, because that would mean writing (derived, but actual) fanfic about the event in question.

In the PPC universe... dunno. I'm not sure there's a theoretical foundation for quarantining, unless it's 'authors can create impenetrable creativity shields by author fiat'. Looking at an easier scenario where it's a specific character who's forbidden: would the story be missionable except for the scene they appeared in? Would that scene be missionable, but the character is an automatic replacement? Or just a moving void where the forbidden character would be if the badfic could 'access' them?

Probably best not to think about it.

hS