Nah, Law's role in the story post Dressrosa is odd,though I could buy him returning to the story at this point now that we have a global flood/war plot. But I don't think Oda really tried justifying him being in Wano and fighting.......Big Mom? Besides the fact that he had the alliance, but mind you, the pirates were not forced to fight the Yonko, they were offered to work under them, and it feels pretty dumb that Law would go from wanting to create a plan to have Doffy be taken out, to just going along with a raid he didn't even plan. You could justify it if you built a connection between Law seeing the people of Wano suffer, and the fact that he himself suffered a genocide, but that just didn't happen. So Law is in Wano in a war about great pirates(which he doesn't really seem to care about, as his actual goal in the alliance was taking down Doffy) and Samurai(which he doesn't care about, unless I'm missing something?). To be fair, I know that he wants to know about the D through the poneglyphs, but I don´t think that´s enough, especially since that goal was only really made a thing towards the end of Dressrosa.