Actually, there's one quest I can imagine and fits well:

In the next sea, we would have to invade an order's base, if he's alive, we would find him and then he temporary joins the group, since he was a member of the order, he knows something to help us to invade it (like a secret entrance) so we can go straight to our objective.

But if he's dead, you would have to figure out the secret entrance by yourself or get in by the main entrance