That's unfortunate to hear. I wonder how far along in the process he was for this film. I don't usually notice editing techniques in movies (though I'm sure it's a valuable, if thankless job) but I wonder if it'll be apparent if they changed it partway through.
Rest in peace, Mark. My thoughts go out to his family and his friends. I see on IMDb that he has been replaced by Adam Gerstel. Always remember a movie is made three ways: when it's written, when it's shot, and when it's edited.