Is it all a dream? Is most of it a dream but bits are real. Which level is Mal on and which is Cobb?
The truth is absolutely any variation is possible for any viewer. The entire system of gaging whether you are within a dream or within reality is based on using the totems and there is no support to the belief of what the totems prove. Mal was the intuitor that decided the totem does one thing for the owner in a dream and another in reality, but if Mal was wrong, then there is no knowing which time you are in a dream and in which you are not. Like when people believed that the Sun went around the Earth because of some basic intuitions on information presented a certain way, Mal may have been lacking some extra information about the totem. The totem and its unique nature may been something in reality but in a dream is has no physicality, the laws of physics do not necessarily work in the dream just because the dreamer knows what his totem should do or not do. What if the deciding factor is what happens to the totem in a dream is not the totem but the dreamer needing the totem to reflect one desperate belief or another? Not necessarily what is best for your mind, what on the surface what might be the thing that would make you happy. Like Vanilla Sky and it's original source, it may be that any number of psychological imperatives could into play, including a need to punish yourself, or some horrible deepseated urge that the individual cannot face. Hypothetically, Cobb may feel what he did to his wife is so terrible he never ever wants to get back to a happy life, get back to his family. Even more tenuously hypothetical, Cobb may be a man who hated being a father, was unsatisfied with being tied to a family, to stability and security, he may need to pretend he desperately wants to get back since it would allow his conscious mind to believe he is a good man, good father, but in reality his subconscious is happy to keep believing he is in reality and trying to get back to his family, as opposed to in a dream, in some level of limbo and his family seperation is entirely constructed in a very complicated way. If such a hidden complexity existed, then it would be perfectly possible that after the ending (specifically Cobb being reunited with his children) Cobb's unseen future would be filled with a stream of intricately engineered obstacles to family togetherness, his subconscious constantly creating new ways he could be seperated from them in his dream world, perceiving himself consciously as feeling anguish at the seperation but deeper, feeling relief and comfort. And any number of variables of motivation therein. Hypothetically.