Once the chief is gone, the Goblins in the northwest camp won't be a threat.
The Goblins will detest humans even more after we kill their leader, so wealthy people won't be able to negotiate any deals with them.
We must defeat the Goblins' leader.
If we can eliminate the trust Goblins have in humans, they won't dare try to sell any of the mystical Fountain of Youth water to anyone.
Thus, we can indirectly stop the plans of any sinister person who plans to slurp down the potion for their own selfish, or possibly evil, purposes.
But I'm not even sure if the legends are even true. Does the Fountain of Youth work?