I think the whole argument here is that Apple has always kept predecessor models around (you can still buy an iPhone 6s and 7 even though iPhone 8 is out, for example) but this is possibly not going to happen with whatever replaces iPhone X. People of course misconstrue this information to mean iPhone X is doomed and so Apple is killing it. Clearly that’s not the case. As you said, they’ll just replace with with a newer version.
It is true that Apple typically kept the previous years flagship and sold it at a lower price. As pointed out, the iPhone 5 was one example where Apple didn't -- and instead offered a different "low cost" option rather than continuing to sell the older phone (the 5c).
My impression is that the X replacement is going to be priced somewhat lower than the X; my guess is $100 less, or so. The rumors, at least that I've seen, seem to imply that the X Plus (the new larger OLED iPhone) will be roughly the price of the current X, that the X replacement will be $100 or so cheaper. Because of this, it doesn't make sense for Apple to continue to sell the X -- since the old phones are typically only $100 off, meaning the X and the new iPhone would sell for essentially the same price. Instead, they'll have an LCD version of the X that will become the new "budget" phone.
We know one of the ways the new iPhone will be less expensive is that they'll have LG panels instead of Samsung panels. I also wonder if they won't have an aluminum body, rather than the Stainless Steel of the X. And the Face ID technology should now be cheaper, now that it is a year old, than it was for the X.
My issue with these iPhone X being "cancelled" or "killed" stories is that they largely came out in February and early March, along with the articles about how disappointing iPhone X sales had been. The clear implication that these "experts" seemed to be painting is that Apple was going to kill the iPhone X because it had been such a disappointment; again with the implication that it would be replaced by a new design, likely bringing back a fingerprint reader and home button, not to mention the notch (though they never explicitly stated these things, but again, they were implying the iPhone X was a failure).
Of course, since February we've seen a number of new phones announced with notches (including rumors of Google's own Pixel 3) and we're seeing Android P will include gestures without having/needing a physical home button (and most Android phones, while they still have a fingerprint sensor, aren't using that as their home button).
To me, the idea that Apple is cancelling the iPhone X is debunked. Yes, it will be replaced as, from what I can tell, economically it won't be practical for Apple to offer it at a lower price than its replacement. Instead, they're keeping the features of the X (even the controversial ones), and offering a direct replacement that appears to look the same (or extremely similar), along with a larger version and a "cheap" version that uses an LCD display.