My group's going to finish 3 Faces of Evil next session, and I've going to go with a variation of the Faceless One is a Similacrum of Darl idea.
In my campaign, Darl has his own agenda (so far undefined) which is separate from the Ebon Trid and the coming of the Age of Worms, but will come across the path of the PCs more and more.
I'll have the Faceless One's death trigger a programmed illusion of melodrama, introduceing himself and promising doom to all the PCS. Darl himself will be made aware of the PCs existence at this time, learn everything there is to know about them, and promptly dismiss them as beneath him.
Then I'll have the PCs find evidece throughout of his presence, and build him up as a major threat, but meanwhile, Darl has bigger fish to fry and so will not be paying any attention to them.
So his attitude on the island will be along the lines of, "Oh yeah. These guys. *Shrug* Well, best kill them."
Something along those lines.