Even if the wedding ring thing is true (which I have my doubts on), it doesn't really matter because Leo does come to term with his wife's death in the next-to-final scene of the movie, so he could very well still be dreaming even if he doesn't have his wedding ring on.
I think the definitive answer would be how his kids are dressed. If they are dressed in the same clothes they had on during his dreams (which are the last way he remembers them looking), then it would be a pretty strong indicator that he's still stuck in limbo and never got out. I'll have to rent it when it comes out on DVD again or something so I can take some screencaps.
