Not related to inability to speak, but it definitely relates to whether dialogue is necessary: something like a year or two ago I read a novel which didn't have dialogue at all. The characters talked to each other, sure, but it wasn't written as dialogue. It was written like "A and B both decided to order coffee. After that things got heated as their intercourse evolved even more political. A seemed to think that..." etc.Not sure how to weave the prologue into the rest of the story. Also, when three of your characters are unable to speak, dialogue goes out of the window...think I may have shot myself on this one.
It was quite slick, especially when it took a while for me as the reader to even notice it's not written as dialogue usually is