Actually I view it as the opposite...
Chances of the enemy winning this war is basically NONE storywise
Oda would earn my respect if the war ended with our loss... and Luffy suffers another MAJOR defeat in this war after Marineford...
Can you imagine if Onigashima will be the equivelant to "Saboady arc".... where Luffy and co basically desperate and try to run for their lives... and what's more... a crew member dies before reaching his/her dream!
Can you imagine... something of that magnitutde happens... and Luffy and the rest of the crew... escape by the skin of their teeth... get away from the place while they are on the brink of death!
And then Wano gets to be free because Kaido and Linlin decides to take on the world... so they leave Wano/Onigashima.... so that is Oda's way to solve the Wano getting freed from their tyranny..
And then... Kaido and Big Mom.. both collect their army.. with all of their crew... they set their eyes on the NAVY to take them down!
Can You imagine "Beast Pirates + BMP vs Navy and WG" where Luffy and his crew + SH Grand Fleet end up trying to get involved in this Large Scale War... and they side with the WG/Navy... because they hold a grudge against Kaido/BM for losing a Nakama
And we have even Garp getting involved because he has history with BM and Kaido...
Now... that... that would be something AWESOME....
But we all know that the alliance will win this war anyway LOL... so yeah... I will not have speculations that will never happen LOL