If the water existed at the impact site, the heat of impact would vaporize it and throw it off the surface, where it could be seen by ground based telescopes. To my knowledge, no indications of water were ever found. The point here is that the impact speed was far smaller than what IKON's would have been, but it was enough to destroy the LP probe. After impact, Hawk would have been a greasy smear on the lunar surface. Actually, an impact of that magnitude would be visible from the ground, and engineers could estimate pretty well the time of impact.
Gravity goes on forever.
In reality, if you move quickly enough you can get away from a source of gravity faster than it can slow you down. This is called the escape velocity . This is not just a matter of semantics, but a real physical effect. That ends my specific points about the movie. I have a few general comments about it, both Good and Bad.