The FDIC doesn't go above the $250k in that case--the assets cover it. I don't think the FDIC has ever paid above and beyond the insured amount to make people whole
A lot of times their takeovers end up with people being made whole, but because they transfer the assets and deposits into another, healthy bank, and the FDIC makes up the losses in the assets, but those losses are going to be less than if they had just paid all depositors their $250k