Will people still buy the $999 iPhone?

Medium answer: Yes, by the millions.

Long answer: Of course they will. There is a subset of people who will buy the most expensive thing available just as a status symbol. There will also be some that want the newest tech to play with, and there will also be those that need to have the latest devices for testing purposes. This phone will sell just fine. I'd actually be more concerned about the number of iPhone 8's that sell because the X may cannibalize initial sales numbers.