Update on my campaign: My players went first for Harrigan so he was already defeated when we had the fleet battle.
They couldn't scry Grok and Peppery, both good friends of the group, so they reasoned that they were being kept there and wanted to save them.
I allowed them to do it instead of encourage them to play the AP in the right order because I don't want them to feel railroaded.
Honestly, it was equally exciting playing it in the wrong order and Adelita made a much more strong final boss than Harrigan. She almost killed the Cleric. They were not dissapointed because they were more motivated to protect their island than to punish Harrigan, so it was even more epic finishing the book with the fleet battle on their coast.
They took Harrigan as their prisoner and tied him to their flagship mast so he could see his own fleet defeated.
The fleet battle itself was quick and devastating. My players did great and they had an overwhelming victory. Most of them are CHA casters so they are able to control huge squadrons but they didn't have as many ships as they could. I enjoyed GMing the fleet battle and my players enjoyed playing it. Much better than the naval combat rules.
Now starting the last book soon!