How do they make documentaries with uncertain outcome

I'm not sure about the specifics in this case, but typically documentary editors have to work with massive amounts of footage compared to fiction editors. The narrative is generally formed in the editing rather than at the filming stage. (Unless it's a historical story, obviously).

I used to want to change the world. Now I just want to leave the room with a little dignity.

Maybe someone pulled a few strings :)

I was at a private showing with the director and she said they predicted which people had the most likely-hood of winning, and also had interesting stories to tell. So they decided to film those people. I think they did actually film one or two others which weren't included however.