He's not trying to get the company back, he's suing the U.S. government for damages. The suit will never be settled as long as the lawyers have a large enough pile of money to draw from. Sort of a modern version of Jarndyce and Jarndyce.
Although AIG itself should have no liability because if the government loses the suit it will be based upon a criminal action committed by the U.S. government. That let's AIG off the hook for damages should Greenberg win.
But even with that said, there is no doubt that as long as the suit remains unsettled it will continue to be a heavy weight on AIG's share price.
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