Yes, hell is necessary to Christianity because Jesus taught concerning the reality of hell, as did the apostles and prophets. The Bible being God's verbally inspired word to men, written through the prophets and apostles, by the Holy Spirit, His teaching is cohesive and without error, and cannot be broken, since God Himself is infallible. The Bible therefore is infallible and inerrant, in the original autographs, has been preserved by God's Providence throughout history, and is able to make men wise unto salvation, having the message of salvation by the grace of God alone, through faith in Jesus Christ.
Salvation is primarily a salvation from sin, and Jesus saves from the penalty of sin, the curse of the law, which is death, and the second death, which is being cast into hell, a place of unquenchable fire, where the wrath of God burns against the wicked forever and ever, because of their sins.
Furthermore, we learn from the Bible that not everyone will be saved, but only a remnant, though a very large number of people throughout history. And it is not possible that everyone could be saved, because God elected some to salvation before the world was in existence, and chose not to save the others. He created some for glory and others for destruction. This is the doctrine of double-predestination, and the Biblical account will be found to support this doctrine.