What a fiasco.

A "merger of equals" between Publicis Groupe and Omnicom Group that was to be the largest acquisition in advertising history is now off as the two companies have proven unable to overcome a range of impediments, including tax concerns, integration pain, and the personalities of the chief executives.

"The challenges that still remained to be overcome, in addition to the slow pace of progress, created a level of uncertainty that was detrimental to the interests of both groups and their employees," the companies said in a joint statement.

The $35 billion deal would have combined dozens of agency brands, including Omnicom's PHD, OMD, and Resolution Media and Publicis's Starcom Mediavest Group, DigitasLBi, MRY, Razorfish, and Performics – to name just a few. With its cancellation, legions of integration committees will drop what they're doing and get back to the work of building client experiences. Or not, in the case of teams servicing clients who have taken business elsewhere out of competitive concerns.

In the programmatic arena, the merger's cessation means the holding companies' trading desks – Omnicom's Accuen and Publicis's Vivaki AOD – need not undergo a "Highlander"-style reckoning. The acquisition had fueled speculation that the combined holding company would keep one and shutter the other, or use one as a "conflict shop" style trading desk to allay competitive concerns. None of that matters now, and that may come as a relief to some of Accuen's 200 or so employees and Vivaki AOD's 250, as it allays the need for a long and no doubt cumbersome integration.

Another happy camper is Sir Martin Sorrell, CEO of WPP Group, who retains his crown as chief of the world's largest agency holding company for a while longer.