Law is so far away from the rooftop, i honestly thought luffy, kid and law would meet each other at the top and fight together kaido but it doesn't look possible at this point. I'm more and more thinking that a group fight against big mom is possible with zoro, law, marco, and co.. that would be awesome.
Btw kid building up his arm for kaido makes it even less possible to fight a calamity in my opinion.