Most of the “ X versus Y” chapters finish the fight either that chapter or the next, so it’s probably over next week. Certainly it’s been the pattern on Onigashima, the only exception is the rooftop fight. But that wasn’t an endgame fight, this one is.
Kid and Law have to win because that’s kind of the point of Onigashima, for the Worst Gen and crews to beat the old gen and crews.
A delay and serious damage to Big Mom victory seems more likely than a straight knockout victory with the dialogue this chapter.
If it just a straight case of Kid and Law outright beating her next week, I‘ll be very unimpressed.
Kid fans should hope for the delay option because it allows for the possibility that for the grand finale it does turn into Luffy and Kid vs Kaido and Big Mom, with them winning at the same time.
Law I think will be done regardless next chapter. Anything else he does will be more using his powers to save the day, not fighting. Him and Kid have been pretty equal so far, slight advantage Kid in panelling more than anything else, but I think if the fight is to continue past next chapter Oda will want to focus on Kid over him.