@Edent Here's what I'd do:
Imagine if the FOI comes back with the most boring, non-story answer possible. Is there still a story?
If so, publish now. If the FOI comes back making the story bigger, publish an update ("Breaking news: Big story is Even Bigger!"). Even if it just confirms the story in the details, update ("FOI proves it, Story is True!"). And if the FOI comes back as a nothing - no need for an update, the story stands on its own.
If there isn't in that case--wait for the FOI.