The idea that you won't see half the screen is a bit misleading. You're making it sound like a movie that was designed to only work in IMAX and was then crudely cropped to fit a regular screen.

That's absolutely not how this is done. Instead, they design each shot to work just fine on a regular screen. The IMAX just adds extra space and spectacle at the edges. You get a broader vista, but the actual scene and characters will be the same in both.