This is a subtle thing I noticed but Mal is French and her name translates to "bad". I was looking at the Hans Zimmer's score and the title theme is a modification of a French song from 1960 by the name of "Non, je ne regrette rien" which roughly translates to "I will live no longer with regret". I went and looked into the lyrics/meaning of the song and was surprised to find an apt metaphor for the movie. It is a song about moving on from a lost love. It also addresses "mal", through the singer's perception of good and bad as only relative. The bulk of the song is about ridding oneself of the haunting memories of that lost love. I think Hans Zimmer deliberately chose this song not only for its tune, but for its metaphorical content. The track is played unchanged in reality scenes and slowed down in dream scenes, thus representing the (seemingly) dualistic nature of his relationship with Mal. In the end, I believe he finally achieves self-Inception, such that he is able to successfully psychologically integrate both the "good" and "evil" aspects of Mal (and himself) and his relationship with her, relieving him of his guilt. The process does not neccessitate the ending of the film to be in either dream or reality, the point of cutting away from the wobbling top is that the nature of being is subjective, and ultimately it did not matter whether the top falls or not, but that through the journey he finds a kind of catharsis. Here are the lyrics to "Non, je ne regrette rien", and further analysis of the ending.
No, nothing at all, I regret nothing at all Not the good, nor the bad.
It is all the same. No, nothing at all, I have no regrets about anything.
It is paid, wiped away, forgotten. I am not concerned with the past, with my memories.
I set fire to my pains and pleasures, I don't need them anymore.
I have wiped away my loves, and my troubles. Swept them all away. I am starting again from zero.
No, nothing at all, I have no regrets
Because from today, my life, my happiness, everything, Starts with you!
So the ending of the song may actually be a subtle breaking of the fourth wall, directly addressing the viewer who, in order to achieve a sense of resolution, is compelled to fabricate a reality external to that of the film which is cogruent with their expectation. The impulse of the viewer to subconsciously not only engage in the fiction but, frustrated by a lack of resolution caused by the "loss" of the ending scene, is to then actually fabricate one's own contribution to the narrative; analagous to the way in which Cobb seeks resolution of loss through subconscious fabrication. The repercussions of the viewer's impulse are negligible, relative to the fiction. The tasks and events of the movie are as supremely complex and difficult as the gravity of Mal's death. The leap to her demise, fatal or not, pulls her so far from his expectation, upon which his subjective reality is built, that in order for achievement of congruent resolution, it required the confabulation be embued with sufficient force as to overcome the tremendous inertial dissonance and angst created by existential attachment.
I have more essays and thoughts about Inception from various philosophical and psychological approaches if anyone is interested in more rigorous discussion of the film, I would be interested in starting up dialogue. You can reach me at firstname.lastname@example.org