As surely as the inspiration of scripture is God's work, so is the preservation of the same. We know God will preserve his scripture, every sacred word, because he promised he would in Psalms 12:6-7.
The words of the LORD are pure words: as silver tried in a furnace of earth, purified seven times. Thou shalt keep them, O Lord, thou shalt preserve them from this generation forever.When God promises something, you can bet that it is he that is finally responsible for it. And since here we have a promise, inspired by God, that his words would be available to us in purity for every generation of time, our confidence is a confidence in God and not in man. So there can be no question as to whether the full testimony of God to man is with us in human language, it is only a question of if we have that witness in the language we understand. And the answer is yes. God has commanded us to desire the sincere milk of the word, and to contend for the faith once delivered to the saints. It is an evident providence that God has blessed his church in our country with the ability to obey those commands as the pillar and ground of the truth, (1 Tim 3:15) and to be throughly furnished to all good works (2 Tim 3:16).