If you watched the film please read
If Cobb wasn't dreaming that means everything ended up good, except for the fact that his wife died.
But, if Cobb WAS indeed dreaming, that means that his wife was right and she's alright, although he is a complete moron and is still stuck in limbo. OR, it could mean that Mal maybe didn't even exist, and the movie was just a very weird dream he had.
I don't believe the whole Mal was right is anything legitimate. I'll requote one of my ealier posts.
Mal really did kill herself though. The basis in the movie for telling what is real and what is the totem and if it spins or not. In the scene where he calls home he spins it and it falls, and he gets on the phone with his daughter or something and it gets explained that he can't go there and such which makes it pretty concrete that Mal is dead. Now in the scene where Mal kills herself it is probably intended for the audience to think "what if Mal is right" but that is there more to make you think and question your own reality. What that scene is primarily for though is to demonstrate one of the first real lines in the movie, that an idea is a resilient virus.