The 17 staff, who worked on the General Mills account, quit after Mike Burns, who oversaw the account, left the agency.
Burns is under contract to Saatchi & Saatchi until March 15, but has admitted that he has "opportunities".
Those opportunities could include founding a new agency at Interpublic to take on those General Mills brands currently held by Saatchi & Saatchi, including Cheerios, Wheaties and Green Giant.
Another option could be setting up a New York branch of the Interpublic-owned agency Campbell Mithun, which already works for General Mills.
Burns, who had been with the Publicis Groupe-owned agency for 25 years, was the joint chief executive of Saatchi & Saatchi New York until last September.
However, worldwide CEO Kevin Roberts hired executive creative director Tony Granger and Arnold Worldwide's Mary Baglivo to take over the running of the agency, leaving Burns to step back to the role of managing the General Mills account.
Following the mass walkout, Saatchi & Saatchi has said it is confident it can hang on to the General Mills account.
"We will continue partnering with it to create big ideas that transform General Mills' brands and take the business to even greater heights," the agency said.
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