Regardless, Law is the catalyst to this entire post timeskip Saga, starting from when he destroyed the SAD factory. Kaidou has had his eyes on both Luffy and Law since then.
Law is a key player here whether he likes it or not, since he started this whole thing, he has to see through to its end, Kaidou himself will make sure of it.
Yes, Law has to be here. But he's also seen a dramatic reduction in screen time and plot importance since the Punk Hazard days, because Law's grudge against Doflamingo was way more important to his character arc than his attempt to take down Kaido.
Kin'emon and Momonosuke are really just as much a catalyst to the post timeskip as Law. And unlike him, they're the ones that really matter in Wano. In essence, their role in Wano is what Law's was in Dressrosa. Take Law out of the series, and Luffy still pretty much follows the exact same path- fights Caesar, that puts him at odds with Doflamingo and Kaido
Now, this doesn't mean that Oda's just going to throw Law (and Kid) to the side. They'll obviously do
something here. You can at least guarantee they'll get a chance to fight Kaido. But ultimately there's more to the series than just fighting. The two of them have been pretty much sidelined so far. If they do fight Kaido, well, this is no Doflamingo. Oda hasn't built up a huge, personal grudge between Kaido and the two Worst Gen kids, it's Oden's lot that got the thirteen chapters long flashback. For all Kaido has ranted about Luffy and Law... he didn't really give a fuck when Law was in his grasp. He had the bigger fish with Luffy, so he just left Law for next time. So even with them trying to fight Kaido, there's very little suggesting they'll actually even do as much as Law accomplished against Doflamingo.
When it comes down to it, I just can't see past the end of WCI, where Oda catapulted Luffy past Kid and Law. It's very hard for me to consider them serious factors in taking down Kaido when Oda has propelled Luffy so far in front of them, and then ignored them for most of the arc. I really don't expect any more from them than getting a fight against someone else (Apoo and Hawkins maybe), winning that, jumping in the fight against Kaido when Luffy's in a pinch, getting a good hit in then getting blasted aside by him as hype. Which incidentally, I also think will happen to Zoro- difference being, Zoro's actually been involved in the rest of the arc and will be involved in getting rid of Orochi to boot.
End of the day, when Dressrosa finished Oda gave Luffy and Law equal bounties. They were only thirty million above Kid then, who'd been above them before. Back then, they all made sense as being rivals of a kind, even though we knew Luffy was a wee bit in front at least. End of Wano, really don't see Oda treating them with that parity.