They already know Kaido's and Orochi's nature. I do believe that Kaido and Orochi are probably falling in Wano land but I just doubt the alliance has the resources or the means to go onto another war.
For Big Mom the marines are a possibility or he could just dumb her down (memory loss or hungry pangs) as he already did many times.
But I am strongly against the idea that the alliance will suffer some utter defeat in Onigashima just to go on to another war after, it is possible but I doubt it, even some beast pirates fodder said some chapters ago that this is their best shot.
Not all of them. There are surely still people who believe in Orochi's propaganda or are too submitted or broken or afraid of Kaido to rise against him and Orochi.
And I also think that we have only seen the tip of the iceberg of what he and BM can do and that the alliance will get a brutal wake-up at Onigashima.
I also imagine that BM's story may continue after Wano and return to Elbaf, though it's possible that Oda may do another twist with her to stop her from being an antagonist or at least have her separated from Kaido in Wano final battle by having her fight the marines or someone else.
Though I think I have already debated enough about it today so let's agree to disagree if you're okay with it.