That doesn't mean Downey will be back. He's on record saying multiple times that he was tired of the character and wasn't wanting to play him anymore. He did agree to return for the next Avengers movie but that doesn't guarantee he'll do another Iron Man movie. A generic sniplet put at the end of a movie, long before any agreements have been made or contracts have been signed is not, in fact, evidence that Downey is returning. Hell, "Iron Man will return" could mean he's returning in Avengers 2.