Thanks, I wasn't sure the exact code to remove them from the world.
I did change the code myself but instead of removing the duplicate, I set it up to prevent the slave granting a reward from being added to the world list until you don't (or fail to) recruit them after the fight.
There was already an if statement that primes the reward at line 539 of the mod file, I added an else and moved the code that adds the slave to the pools there.
Then I duplicated the code to add them to the world in the reward section at the end of every scenario other than successful recruitment.
It seems to have worked fine so far and has the added benefit of not posting a message about maybe seeing them again until after they leave.