A more likely scenario would be that Luffy is more or less top dog of the world in fighting prowess after defeating the Yonko and becoming Pirate King, but Gear abuse and the adrenaline he received from Ivankov proves to be his undoing, weakening him enough that the three admirals are a challenge similar to what happened with Whitebeard. The ending will most likely be that Luffy and Dragon announce that the age of the World Government has ended, and each nation will now be allowed to go its separate ways and the erased history is revealed as per Robin's wish, with Luffy perhaps feeding his kid the Flare-Flare fruit if Sabo has died by then in memoriam of his two brothers.