The German executive was brought out to Asia to oversee the integration of the WPP-owned Batey Ads network into the Red Cell network.
Dietzel, who will not be replaced, was appointed as chief executive officer of Red Cell Asia-Pacific last year. He was previously managing director of DDB's Berlin and Beijing offices.
The job of integrating the network will now be handled by Rod Pullen, the Batey Group CEO and Jon Collins, the Batey chief operating officer.
Dietzel was given responsibility to build the Red Cell brand in the Asia-Pacific region through acquisition and organic growth.
Although Batey retains its name, any new agencies that are bought will take on the Red Cell name.
The Red Cell network now comprises the Batey Group in Asia; what was Conquest in Europe, which has been rebranded; US agencies Cole & Weber and Berlin Cameron, which have also taken on the Red Cell name.
Earlier this year, WPP boosted Red Cell with the acquisition of London-based research and strategic consultancy, HeadlightVision.
WPP, headed by CEO Sir Martin Sorrell, has long been rumoured to be in the market for a creative agency in London to beef up the offering of its Red Cell network.
In April, Red Cell's London operation moved into the Isleworth-based offices of Perspectives, its below-the-line sister agency, in an attempt to cut costs after losing the Direct Car Finance account.
In December, WPP bolstered the US operations of Red Cell when it bought the US advertising agency Berlin Cameron & Partners, which became the New York City office and headquarters of WPP's Red Cell network. It also named Lee Daley, the former McCann-Erickson chief strategic officer for the Middle East, Europe and Africa, as the chief executive of Red Cell Network.
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