Final War. Post Laugh Tale, Luffy will find out the "key" to defeating the WG with the Revolutionaries and his massive alliance. Blackbeard, with Pluton, sees his opportunity to destroy the WG with his allies. Basically a 3 sided war.
In the end, I half expect Luffy to use the ancient weapons himself and destroy Mariejois intentionally. Sunlight Tree Eve will die, and the redline will crash on FI.
Noah will be used at this point to save everyone. Jinbe will be the one to actually revisit FI and possibly fight Vasco Shot and/or whomever else at the time since it's his dream to save his people.