Re-reading this post, I realize there are other issues that I didn't mention. For example, if the hunter is from Baldurs Gate, why ask this hag who lives 200 miles outside of the city for help? Surely there are better resources in BG itself. Maybe he is a local mercenary that heard about the job on some sort of magic-weave based job-posting-board for bad guys?
Even then, how much does this guy stand to get paid? I don't see your average mercenary giving up their soul or one of their eyes for a single contract. Even if it pays enough to retire on, if others are also searching, there is not guarantee he would be the first to reach the target and get paid. I know it is a video game, but none of this adds up and it just feels very forced.
If he/she was already hunting Astarion and got abducted along with Astarion, that would be different. And honestly that would make the most sense. Right now there is a Tiefling you run across who was on the ship who is not a companion option. So maybe they could even go that route if they don't want to deal with all the work that goes into a full blown companion. Have the hunter be someone who was on the ship, but not a companion option.
Anyway, trying to help with some suggestions. But ultimately if it gets fixed, I'm sure Larian will do their own thing. I just hope they do something.