No more guesses?
Recap of clues.
1) *After* this episode something disappears forever.
--6) That is a feature of a main character.
2) Something that has never happened before.
--7) In all of history, and it later has major consequences for a main character.
3) Something never happened.
4) A method of detection that never works again.
5) Somebody is not who they appear.
--6) Not metaphorically, not the "kind" of person they appear, they are literally a different person than they appear to be.
Clue 8) The thing that never happened is a political event. And the method of detection never works again because every future attempt is faked.