WOW, my deepest respect for allowing your players to influence Plugg. Unfortunately, I was less fortunate.
I did manage to capture Plugg alive and keep him as a prisoner, but I didn't have the backup of my GM. He told me that Plugg was hostile and would remain hostile after I was part of the crew that stole his ship.
In return, my action of keeping Plugg and not killing him made Sandara hostile towards me.
At the end of the campaign, the GM wanted feedback and I told him that I didn't think it was okay that I was allowed to affect every damn NPC except Plugg.
He just told me that Plugg is the enemy according to the book and that he only played according to the rules. I was lucky Sandara and Cog didn't try to stab me at night, he said.
But our Conchobar has had an interesting career.
In the storm at the beginning of the adventure he went overboard and all attempts to save him failed.
We then threw a few empty crates and barrels overboard, hoping he would reach one so we could pick him up again after the storm.
He did reach one barrel, but he sailed it all the way to Tidewaterrock, and became the new steward there. When we got there, we got a nice bonus because he put in a good word for us.