Relatives can still interfere and try to get that money back. If they've studied previous cases where relatives didn't want a cryonicist in the family to go into the dewar, they could cremate the body first, and then demand a refund because that breaks the conditions of the agreement between the cryonicist and the cryonics org. Burying the body conventionally is not sufficient; Alcor has won at least one case to exhume a body and straight-freeze it any way, while still getting paid..