Complex sentence: Although he has lost all his money, Sam holds out hope that Barbara will now definitely be killed--because (according to the kidnappers) if anything went wrong, they'd kill her, and he'd inherit her $15 million fortune.
Split into simpler sentences: Although he has lost all his money, Sam holds out hope that Barbara will now definitely be killed. According to the kidnappers, if anything went wrong, they'd kill her, and he'd inherit her $15 million fortune.