Not to mention, if we look at the costumes of the children it can be surmised that he's in reality. In his last memory consisting of his children, his daughter is wearing an all orange/red dress. His son is wearing a plaid shirt consisting of blue and red colors. At the end, the notion is if it's still a dream, his children should be wearing the same clothes as they do in his last memory of them. His son is wearing the same shirt, but his daughter is wearing a dress that is also orange, but it has white sleeves. If we go based off a production cue, then he's clearly not stuck in his dream.
And although it didn't fall, we can infer from the top that it likely wasn't a dream state. Throughout the whole film, the top spins perfectly in the dream world with no shakes or blips. Yet, at the end it shakes and wobbles. It's not concrete, but it's another clue we can use to jump into the mind of Nolan.
Of course this is all a moot point until Nolan himself specifies what happened at the end.