Mission Accomplished
In the course of their journey to the Goldtooth Fortress City, Samiel and Yvriane were having an enjoyable conversation as they discussed the previous mission for The Guild. Unfortunately, they didn't succeed in procuring the slaves since Samiel's Undeads had destroyed and killed everything in their way.
It is not likely that anything else could have been done because, from what he knew, they would be practically worthless as slaves because their lifespan was limited to only a few months, and no legitimate slave trader would buy a slave whose lifespan was only four to seven months.
If you were to invest in slaves like that, you'd probably end up with a bad investment, considering that slaves were mostly purchased to provide labor. Still, there were also some species that bought slaves for the purpose of food, experiments and ritual material, as well as for the purpose of performing experiments on them.