Yes, he did preserve it.
He keeps it mostly in the minds and hearts of non-Catholic, non-Protestant, non-denominational believers. I say this with certainty because the organizations of men are inevitably going to be corrupted by godless, Spirit-less men who crave positions of authority. It's a given. That's why I contend that the true church of God (the nation and people of true believers) is not identified and contained in an organization at all. True believers are intermingled with the nations and peoples of the world at this present time and won't be gathered together as the organized body of God's people until the end.
More opinions.
And you are implying that Jesus failed to keep his promise for 1500 years until Martin Luther and his merry band came along.