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Thorsten Heins, the chief executive of BlackBerry, will leave after the collapse of a tentative takeover offer from BlackBerry’s largest shareholder, the company said Monday.

Instead of purchasing BlackBerry and taking it private, the largest shareholder, Fairfax Financial Holdings, and an unnamed group of institutional investors will invest $1 billion through debentures that can be converted into common shares at a price of $10 a share.

Shares of BlackBerry closed down 16 percent, or $1.27, at $6.49.

There has long been skepticism about the ability of Fairfax to turn its tentative offer, which values BlackBerry at $4.7 billion, into a firm bid. Since it first made the offer in September, shares in the ailing smartphone maker never rose to Fairfax’s $9 a share price.

John S. Chen, the former chief executive of Sybase, will become BlackBerry’s executive chairman and acting chief executive.

Along with the cash infusion into BlackBerry, V. Prem Watsa, the chairman and chief executive of Fairfax, will return to the phone maker’s board. Watsa had resigned after the company announced that it was reviewing strategic options, including a sale, in the summer.

Heins, a former Siemens executive in Germany, became chief executive in January 2012 after James L. Balsillie and Mike Lazaridis, the longtime co-chairmen and co-chief executives, resigned in the face of a rapid decline in BlackBerry’s business and the failure of its PlayBook tablet computer.

Formerly the head of the company’s handset business, Heins heavily promoted the new line of BlackBerry 10 handsets as the company’s salvation. They proved, however, to be a commercial failure.

Chen led Sybase from 1998 until the company was acquired by SAP of Germany in 2010. He is widely credited with saving Sybase from bankruptcy. When he arrived, Sybase had lost much of its corporate database business to Oracle, IBM and Microsoft. Unprofitable, it had also developed a reputation for producing unreliable software.

It’s not clear if the investment by Fairfax will affect an attempt to make a bid for the company by a group that includes Lazaridis and Douglas Fregin, the other co-founder of BlackBerry, as well as Qualcomm and private equity firm Cerberus Capital Management. (Qualcomm makes the chips inside BlackBerry phones.)

Other companies have also looked into BlackBerry as a potential acquisition, although it is not clear if they have any interest in a bid.