As soon as Big Mom sees Luffy, she will want to fight him. Thats the sole reason she even came to Wano. The alliances target is Kaido, but its not like they have much choice when their front man is Mamas target as well, so a fight vs 2 emperors is unavoidable. Right now its Luffy, Law and Kidd, but i expect Hawkins and Drake to eventually tag along (not sure about Apoo, hes yet to be seen in Wano plus i cant really read him. And dont forget Kidd will want to murder him). That gives us a 5v2 which probably wont be enough still, so an outside nerf for the yonkou probably happens. Will they both die after the battle? I dont think so, but i think its the end of their relevance as far as the main plot is concerned.
Off topic but if you go down through the rest of the named, significant characters on either side, i think everyone gets a solo battle. Mama hasnt brough her whole crew, Katakuri, Oven and Cracker most significantly. Kaido is already without some headliners (Udon gang, Hawkins and Drake eventually, Page1?, the fodder Luffy defeated?, Sheapshead, Horselina...). He still has the allstars and 4-5 (depending on P1 status) from the flying six even without Drake, then the other headliners (dont think there are many), gifters, numbers, Orochi and his men. The PMS alliance has enough strong men to match them one for one, where they are heavily outnumbered is the fodder, which Kaido has way more. But nothing coc cant even out