So if i understand you correctly, you are saying that ensured perpetual magisterial infallibility is essential for assurance of what is of God, men and writings. And should I presume that being the historical instruments and stewards of Divine revelation (oral and written) means that such is that assuredly infallible magisterium. Thus any who knowingly dissent from the latter must be in rebellion to God.
Does this represent what you hold to or in what way does it differ?
The word we use is “schism”. Jesus gave us a Church in which to live our daily trust in Him. Jesus built the Church for us, and as St. Paul notes, that Church is become the Body of Christ. If we leave that Church, or reject its teachings, we place ourselves in peril of losing the Truth.