This whole question is a gargantuan spoiler. Just don't read it if you haven't watched IM3.
The Mandarin calls up POTUS on live television, and 'murders' a man in cold blood.
Did that guy actually die? I think this is the deciding point on which we can determine if Mandarin will return or not. If that hostage lived, it was all truly a hoax and we can resign ourselves that Marvel destroyed an iconic villain blah blah blah...
But if he died, it means that Ben Kingsley's mandarin isn't quite so innocent or bumbling, but actually killed that hostage in cold blood, and just switched plans when Stark showed up in his bedroom. We might yet see a 10-ring powered martial arts master battling an Extremis-based-nanosuit-covered genius in the next instalment!