Shouldn't が be used instead of を since 残る is an intransitive verb?
1 Answer
彼はお金を残らず奪われた。
お金{かね}を is connected here with 奪われた{うばわれた}, passive past form of transitive verb 奪う{うばう} "to steal, to seize".
残らず{のこらず} is adverbial modifier of 奪われた{うばわれた}, it means "without remaining".