According to a recent interview, Iron Man co-screenwriter Mark Fergus is very involved with the day to day production of the Jon Favreau-helmed movie. He says:
"I'm not there to defend what I've written. You have to be open to creative input. That's part of being a screenwriter. Robert (Downey Jr.) and Terrence (Howard) will come up with things - but we want to be sure that whatever they do works for the character and the Marvel universe."
In an interview back in March Fergus mentioned the background reading he did in preparation for writing the screenplay:
"I did read a ton [of Iron Man comics]. I knew a little, but they sent me this huge primer on him, and I read through it and read more and I went online and read more. I felt at some point that I really knew what this universe was, and it was time to stop and looking at the story elements and that was it. Very quickly, I became pretty adept at what the universe was. I'm glad I was coming from the outside, because I could look at it as a story and not something precious and be concerned about breaking certain rules or going certain places, you might be terrified of. Marvel's at the center of it, so they're not going to let you mess with their characters in any significant way they don't like, because they know everything."
So within the parameters of the above comment, he's attempting to keep things in-line on the set and to keep the stars from putting too much of a personal spin on their characters that might take them too far off track. The good news as far as the characters are concerned is that the script is portraying Tony Stark pretty much the way he's always been in the comics:
"He's trying to come to terms with himself, personally and emotionally. It's a breakdown and rebuild. In a way, the film is about a hero who doesn't always make the right decisions."
However fans of the Jim "Rhodey" Rhodes character might have a bit of cause for concern:
"We cover his evolution... He's the only character in the movie with substantial cuts and changes from the comic. I'm excited about it. We've turned him into more of a three-dimensional character."
I have to agree that back in the heyday of the Layton/Micheline era that Rhodey's character was not nearly as fleshed out as Tony's, and that's probably the comic era he's referring to. In more recent years Rhodey's character has been given more depth via the limited War Machine series and other titles, but no doubt those were not part of the reference materials used to define the character.
Finally, in regards to a possible sequel:
"There's been some talk about that... They want to do it. We've talked about where things might go. I haven't been asked yet, but it seems like a natural progression."