Child support is a bit different. The amount owed for arrears is due to your mother. With her gone, she can’t collect, but the debt is not nullified. The amount he was in arrears for must be paid to her estate, which then gets distributed as outlined in her will. The amount paid for the time you lived with relatives while under the age of 18 belongs to them as they incurred the expenses of providing for you.

Keep in mind that, as an adult, they may also charge you rent and require that you fully provide for yourself in all other ways.