It's intentionally open-ended because the camera cuts before you can tell if the top falls or not. American Psycho also does something similar to this.
Inception makes a point of introducing us to "The Kick". You remember the scene. We all remember the scene, because it is crucial to the story telling.
So the plan was to put a guy to sleep, go a few layers deep into the minds of multiple people, all of whom need a kick to wake up...and they decide to do this on an AIRPLANE.
An AIRPLANE. In flight. Across the ocean. All of them dozing off in first class, in various stages of sleep. In turbulent, kick inducing, skies.
Cherry on top - Buddy bought the airline just to make it easier.
Christopher Nolan tries to hide his shoddy writing with flashy edits and quick quips about the plot, hoping to distract the viewer from his lacking skill.
Oh I wasn't trying to imply Inception has good writing. Just that good writing uses that particular technique. Inception is fine for what it is if a bit convoluted