That article isn't really representative of what is happening but I'm sure it's written that way in order to create interest.
AIG isn't looking to file a lawsuit.
A minority stake holder in AIG (12%) has filed a lawsuit because he disagrees with the terms of the buyout and his dilution of shares, etc.. Awkwardly, it's an Investment Group owned by the former CEO.
They've been asked to join that lawsuit. That leaves AIG in a pretty tenuous position.
Technically, AIG has no legal responsibility to the government but they are responsible for protecting their share holders rights. They have to weigh whether his case has merit.
They could end up missing out on a big settlement and being sued by their share holders