If that happens, there is a chance Illinois will no longer be a state and revert back to Federal territorial status, because a bankruptcy will result in the dissolution of state government.
I don't see how that could happen -- you see the federal government is a creation of the several states, so even if a state were to cease to exist, it simply doesn't "turn over" to the federal government. Besides all that, the properties which the federal government can own are pretty limited, as Judge Napolitano observed during the Nevada standoff, as per the Constitution:
To exercise exclusive Legislation in all Cases whatsoever, over such District (not exceeding ten Miles square) as may, by Cession of particular States, and the Acceptance of Congress, become the Seat of the Government of the United States, and to exercise like Authority over all Places purchased by the Consent of the Legislature of the State in which the Same shall be, for the Erection of Forts, Magazines, Arsenals, dock-Yards, and other needful Buildings;—So that's: