It's been a year and a half since John Schaefer was ousted as the chef at Irving Mill, the new American restaurant located near Union Square. (Schaefer was replaced by Ryan Skeen, the rising star who's since left Irving Mill himself and is now running things at Allen & Delancey.) But Schaefer's stint at Irving Mill is now the subject of a contentious, messy dispute between the former Gramercy Tavern executive chef and Irving Mill's owners, Suzanne, Mario, and Sergio Riva.