The cult of Jesus was alive and spreading fast long before the first Gospel was written, Paul's christology vied with others for a good while. The making of the relgion the official one of the Roman Empire is late in the develpoment of the cult, and various branches, the Coptic for instance , were not exactly subsumed.
Faith in Christ was not really heavily joined to the N.T writings until the literalist schools of the late 19th and early 20th century came along. Luther in his time had advocated "Sola Scritura" but this was to stop the excesses of the RC church, charging for "Indulgences" etc.
Faith in Christ was spread initially by word of mouth, as the common people were, in the main, illiterate throughout the subsequent centuries this remained the main method.
Christians like "A Guest" on here do not rely on the N.T to have a living faith.
The JW's would be the least affected, what the Bible actually says has been ignored by them for so long that its demotion to pure fiction, if that were to ever happen, would not matter, their faith is in the Governing Body that they worship.