You're definitely confused, and it's definitely a plot hole created by cutting out Andre's line. Fezzik dunks Inigo's head in the barrels of water, and then Inigo says he needs Vizzini to plan an attack on the six fingered man. "But Vizzini is dead" says Fezzik. And Inigo decides that the Man in Black must have bested Vizzini in smarts, and so he could help them plan revenge. End scene.

Later we see the Man in Black being tortured, and Humperdinck turns the machine all the way up to 11, and the whole kingdom hears him scream. We see Buttercup hears it, and then Inigo and Fezzik walking through a crowd. Inigo recognizes it as the sound his heart made when Rugen killed his father. He deduces that it must be the Man in Black because his true love marries another tonight. Fezzik appears to be surprised by all of this.

There are plenty of ways a throwaway line could hae filled the gap, and it was in th script and in the book. But in the movie, it's a plot hole.

Also fun fact, there is no "unabridged version" of the book, and S Morgenstern doesn't exist. That was part of the conceit for the book. All the stuff about looking for the original and finding it too boring to reprint, that's part of the story. All of the details in the book about Goldman himself are also fictional. Goldman also references additional chapters and a sequel that his publisher has, but cannot publish due to legal complications with the Morgenstern estate.

I love everything about the movie, the book, the author, and the cast.