RDJ's departure from "Gravity" is just the latest setback for the production but shouldn't be a fatal one since his role was fairly minor. "Gravity" has cycled through more prospective female leads than any film in recent memory, though Sandra Bullock may yet sign on.
It seems doubtful that Downey will play a character based on Greven, but The Playlist has a funny-cuz-it's-probably-true guess as to the plot:
Robert Downey Jr. will play a man looking for love who finds all the answers in a little advice book he finds at his nephew/niece’s house. Soon he finds women are giving him another look, but more importantly, he learns that true love is out there for everyone. So there you go Hollywood, we just gave you the logline for a $100 million romcom right there. Please feel free to send us a check.
Robert Downey Jr.: "Due Date " Best Work Experience Ever
What's got us truly nervous about this project is that Downey's wife Susan, who's done a miraculous job reviving her husband's career, will be co-producing with Shawn Levy, a man who thinks schmaltz and pratfalls are essential nutrients.