They discontinued the iPhone 5 after a year. The form factor is still with us though.
When Apple releases a high-end smartphone, they normally keep it on the shelves for three, sometimes four years. What was once a high end model gradually becomes a low end model (Disregarding the X, you can presently buy the 6S, 7, and 8 through Apple directly, and the 6 is still available via carriers).
Sometimes, though, they don't. Apple only kept the iPhone 5 on the shelves for one year - replacing it with the iPhone 5C a year later (which was not perceived as very successful, although it remained on the shelves for the additional two years that the 5 would have remained on the shelves for if Apple had followed their normal cycle).
This did not mean that the iPhone 5 or its form-factor was a failure, though. It went through two more iterations (the 5S and the SE), one of which is still available more than five years later. As far as I understand it, the production cost of the aluminium case of the 5/5S/SE was simply quite high initially, and Apple therefore wanted to make it exclusive to its high-end model for another year.
Could Apple discontinue the iPhone X this year in the same way they discontinued the iPhone 5 after a year? Sure, particularly if they are having trouble sourcing enough of the OLED screens that it uses. Will they release a new model with the same or a similar form-factor as the X this year? I'd wager a large amount of money that they will, whether or not they discontinue the current X.