I'd risk losing potential readers. Editing an existing and basically completed fic to fit canon is a giant drag, as is having to hold it back artificially because of such considerations. You could stagger your posts so that the final chapter is only up when the danger of 'spoiling' someone is banned. You could then draw attention to your fic once more as a non-spoilery one that will hopefully attract the readers who avoid spoilers.

Are there really that many people who avoid spoilery fics? I can see some sense in avoiding sneak peeks and the like, but the stuff that haunts the internet months in advance tends to be misleading. It isn't inaccurate as such, but I feel that whoever leaks it makes sure that it's the most ambiguous stuff that gets leaked so as to create false expectations. I wouldn't avoid fanfic because of that even if I chose to avoid previews or spoilers by people who get to see advance viewings.

I loved 'Three Months' so I'm really looking forward to this.