生け贄 sounds a tad scaring there, I would choose 犠牲(ぎせい). and 自分自身 instead of 僕自身. "is that needed" can be "is that needed or not" here and 必要(ひつよう） suits better than 要る, from my view. I have no idea what "that world" is, so just borrow your word,
「あの世界のために僕は自分自身を犠牲にすることができる。でも問題なのは、それが必要なのかどうかだ。」
"my words" has to be dug deeper here, both 詞 and 言葉 can be understood but still missing something. Can it be put into another way like "It was the question that I had before the battle"? Then it automatically leads "The answer........." phrase in Japanese as well. 有る must be 居る there, plus 存在している is recommended for story telling style. Let me put the last 2 lines together as it is ear easy to me
これが戦いの前に僕が持った疑問だった。答えは「ノー」のように思えたが、悪はまだ、確かにこの世に存在している。
I avoid using the same word twice, so I choose 世 for 世界, and add 確かに（surely） to make it very Japanese.
Anyway my translation seems a bit too novelistic, and sorry it doesn't help grammatically a lot.