The Church has not and CANNOT go off the rails as you put it. It was established by Christ himself and if it went off the rails it would mean Jesus had lied when he said the gates of hell will not prevail against it.
Of course it can go off the rails 
! It must, unless its Shepherd-King preserve it with His inescapable vigilance & power.
Or rather, the Church can speak according to mind of Christ in one respect, while behaving in a totally unChristlike manner in another. It can be guided by the Spirit of Christ in recognising something as God’s Truth, while inviting God’s Righteous Judgement upon itself for crucifying Christ afresh by its of torture and exile and violence & all our other sins. God hears the opporessed, and acts for them - even when those who oppress are His own, & are name by His Name. God’s Righteousness
cannot be deflected or bought.
And it can do that constantly - the Church in the High Mediaeval Period had severe problems with simony. St.Peter denounced Simon Magus with great severity in
Acts 8:9-25, for wanting to pay money for the gift of the Holy Spirit: I can’t believe that simoniacal clerics - including Popes - would not get as severe a tongue-lashing from him. This shows, ISTM, that in the Church there is both the wretchedness of sinful man, seeking to serve only self, & also the faithfulness of God, victorious despite our sins and wickedness. God subdues His sinning people to Himself, by the invincible grace of His Spirit, Who can be grieved, but never thwarted - that is why we are not destroyed in our sins, IMO.
It is **not
the orthodoxy, the good works, the other acts, or any other thing done by man, that is fundamental to the Church: it is the gracious purpose of God that keeps the Church as the Church. IOW, The Church is the Church, not because it is infallible, immune from deviating from the Will of Christ, free of heresy, has an Apostolic Succession, or valid orders, a priesthood, true doctrine, or any such stuff - non of this is of any value or importance, in comparison with the faithfulness of Christ. In fact, Christ has no need at all of Catholicism, none whatever - if the Church betrays and denies Him, if it makes His Good News a means of selfish tyranny and all-too-human pride, He can always raise up a people to Himself from elsewhere, who will obey, will serve, who
will hear what He says. Christ the LORD has no favourites - only we, who are blind, poor, naked, needy & lacking in wisdom, could possibly think that God the King, Whose sole Word sustains the universe, is going to be impressed by numbers or size or junk like that.
What God wants - and must have, no matter what the cost - is Righteousness. His Kingdom is a Kingdom of Righteousness. And if His Church perverts His grace and mercy into unRighteousness, He will vomit out His Church and raise up a people for Himself Who
will be righteous,
not in their way, but in His. The Church does not exist for her own selfish purposes - she exists to promote His Good News & Kingship; her mission, is greater than she is.
Does this make Christ a liar ? No. He cannot deny Himself - so He cannot sacrifice His Righteousness to His promises made to His Church. The Jews received His promises, but they mistook as a giaarantee that however they might sin, the Temple, & the city of God, would stand for ever. They sinned, & persecuted & slew His prophets - so He poured out His fury upon them, and scattered them to the four winds, sending the Babylonians against them, killing their priests, defiling & destroying His holy Temple, ending the kingship of which He had sworn to David, “There shall not be a man lacking to sit upon your throne”. If God’s Chosen People defy Him, He punishes them:
1Pe 4:17 For the time has come for judgment to begin with the household of God; and if it begins with us, what will be the end of those who do not obey the gospel of God?
ISTM that the passages we take as guarantees of the Church’s faithfulness, are in fact guarantees of
His - & that leaves no end of room for us to sin in every way imaginable. It His faithfulness, not ours (which we don’t have, unless He give it) that is the centre of attention. That, & nothing in sinful us, is our one security. The Church must crumble & vanish, unless He protects us against ourselves. ##
