No, if the brother does not show up, then Cook County owns the copyrights and can auction them off. However other heirs can come forward and claim ownership in court.
The negatives are not in play, Cook County has no claim on them, they were abandoned before her death. Maloof and Bulger will never gain copyright without an heir they can buy from.
The rub here is, without the negatives the copyright is valueless, and without the copyright the negs are devalued.
However much later the copyright will run out. (author’s life plus an additional 70 years.)