
As Buggy stated, he has no intentions of fighting the other yonko. His goal is to go straight for One Piece.
As such, whereas the RHP and BBP are bound to fall soon, Buggy will likely be the last yonko to fall.
My guess is, after Luffy beats Teach, he will run into Buggy and the burned man. Buggy will get to the burned man before everyone else as he won’t stop to pick fights.
This will ultimately lead to Luffy’s final challenge before he becomes PK. Luffy will have to defeat the burned man, while Zoro will have to defeat Mihawk.
Overall, Luffy and Zoro’s dreams parallel each other. In the same arc Zoro beats Mihawk and becomes WSSM, Luffy will likely all but become pirate king. I feel like clubbing the burned man with cross guild will be the most logical way to do this.
Luffy will beat the burned man, gain the last poneglyph, and become PK. Zoro will beat Mihawk and become WSSM.