STUTTGART/BERLIN, Germany (Reuters) - Ousted Volkswagen (>> Volkswagen AG) patriarch Ferdinand Piech did not attend a shareholder meeting of the carmaker's controlling clan on Wednesday, fuelling uncertainty about his stake and future involvement in the family business.

Piech, at the helm of Europe's biggest carmaker for more than two decades, was forced out as VW chairman last month over his criticism of Chief Executive Martin Winterkorn, who was backed by other stakeholders and family members.

Porsche SE (>> Porsche Automobil Holding SE), a holding company owned by the Porsche and Piech families, controls 51 percent of VW's common stock, with Piech owning a 13.6 percent stake in Porsche SE.

Sources close to the matter say Piech threatened to sell his stake during the showdown with Winterkorn.

Arndt Ellinghorst, an analyst at Evercore ISI, said it was "crucial" to get Piech back to the table because of an agreement among the Porsche and Piech families to vote unanimously on strategic matters, though he added his return could probably only be achieved via broader management change at VW.

Winterkorn, who is also chief executive of Porsche SE, told the shareholder meeting he was determined to work with Piech as before -- a point echoed by Matthias Mueller, chief executive of the Porsche AG sportscar company that is part of the VW stable.

"We have worked together successfully for more than 30 years," Winterkorn told reporters at the meeting of more than 4,000 shareholders in Porsche AG's home town of Stuttgart.

Martin Weinmann, a lawyer for the Berlin-based Consumer Advice Center for Investors, told the meeting: "An active mind like Piech's is indispensable to hold a major group together."

But it was unclear whether Piech, who also missed Monday's supervisory board meeting at Porsche SE, would grasp the olive branches apparently being offered to him.

Speaking ahead of the shareholder meeting, Porsche SE chairman Wolfgang Porsche said the clan would continue to live up to its responsibilities toward VW. Asked whether that also applied to his cousin, Piech, he said: "Probably yes."

Piech's board seat at Porsche SE was the only office he did not resign when he quit VW on April 25. Porsche family members have a right of first refusal if he decides to sell his stake in Porsche SE, a source close to the matter has said.

VW is in transition, looking for a new chairman to replace interim incumbent Berthold Huber, a former IG Metall union boss, while targeting a new structure for the 12-brand group.

Labour and the German state of Lower Saxony -- VW's No.2 shareholder -- are in a stronger position than before the power struggle. Labour leaders on the supervisory board are pushing for a reorganization that Winterkorn last week pledged to draw up by October, two labour sources told Reuters.

VW, already trying to drive through a multi-billion euro cost cutting program and turn round underperformance overseas, dismissed labour's claim as "idle speculation".

(Editing by Georgina Prodhan and Mark Potter)

By Ilona Wissenbach and Andreas Cremer

Stocks treated in this article : Volkswagen AG, Porsche Automobil Holding SE