One problem I know you didn’t say this but Yamato is not interested in being the shogun of wano. She has already shown she interest go out sea with Ace and friends but she was limited possible doing such thing. Second best choice to Join Luffy instead. Since the one piece world is very discriminatory against people based on their lineage and there bloodlines I don’t think Yamato accept quite Easily. IThey will only see her as the descendent of Kaido that ruined there country for 20+ years. Even though Momo and Shinobu could try voucher for her as person. The commoners won’t see it that way. Yamato could still join the straw hats after this arc. If some nine scabbards do somehow survive this is likely they would look after momo from here on out. Since mink tribe allies with Kozuki they could help rebuild wano as well. Plus if boarder of wano do open she is likely going get bounty on her head. Knowing akainu his sense justice Is absolute he doesn’t mind killing people regardless how innocent their intentions are. He only see her A criminal and an outlaw from another criminal that must be Punish.