crocodile didnt pose a immediate threat to every one in alabasta its different with kaido because of SN lose this fight there is nothing stopping him killings every one on the spot. All crocodile wanted is to get more powerful he didnt care what happens to the people or who opposed him, Kaido on the other hand wants to enslave the people of Wano and will kill any one who opposed him and thats the difference.
Edit: like i said in short it doesnt make sense for the SN to lose if they lose there is no stopping Kaido from killing everyone in wano
Edit: like i said in short it doesnt make sense for the SN to lose if they lose there is no stopping Kaido from killing everyone in wano
Kaido actually isn't trying to kill Wano citizens, unlike Crocodile. The island is going to land eventually.

now to answer the question, first I think a sixth person will also come to the roof (probably Yamato) and will help them. Luffy and Zoro will be the key to defeat him and I think Odas solution was really Luffy mastering ryou and Zoro mastering Enma. Maybe Big Mom will also snitch on Kaido and this will play a big role regarding his defeat.
I don't think big mom is going to be defeated. She will either betray kaido or leave or something