Ryoma Sakamoto died without having fulfiilled his ambition.
Ryoma Sakamoto died before he reached his goal.
この場合、次のような言い方ができます。
ーRyoma Sakamoto died without having fulfilled his ambition.
「坂本龍馬は大望を遂げずに亡くなった」＝「志半ばで亡くなった」
without having fulfilled one's ambition を使った言い方です。
ーRyoma Sakamoto died before he reached his goal.
「坂本龍馬は目的を達成する前に亡くなった」＝「志半ばで亡くなった」
before he reach one's goal を使っても表現できます。
ご参考まで！
カナダ 
