TNA Wrestling issued an official statement on the resignation of Jeff Jarrett. By all accounts this is legitimate and not part of a storyline. Should something change, we'll pass along the word. The official statement is available in its entirety below:
TNA Entertainment, LLC announced today that it has accepted Mr. Jeff Jarrett’s resignation from the company effective January 6th, 2014. Dixie Carter, President, commented “On behalf of TNA, we would like to thank Jeff for his contributions to the Company. We wish him the very best and look forward to his continued participation as an investor in TNA Wrestling."
The statement does answer the question about Jarrett's ownership stake in the company.
You can read the statement in its original format at this link.