Whether or not the top was about to fall is irrelevant. The film stopped before it did and Nolan was making a statment by doing so. If you wanted a definitive answer than this is not the film for you, sorry.
The film stopped the moment we saw the top falling. The belief there is anything ambiguous about whether the top falls is just flat out wrong. If Nolan thinks there was any ambiguity about whether the top falls, he understands nothing about how the material world works. (Which by the way would be a severe criticism of his intelligence.)
However, if the top is somehow imagined to not fall, it means that DiCaprio simply ignored what he told the false Mal about preferring reality. Coupled with Cillian Murphy's fake epiphany about his father's love, the movie quite unambiguously implies dreams/the movies/fiction are just as good as the real thing.
These arguments are astonishingly successful in lowering my opinion of Nolan's talents and achievements.