Good Grief, I hope not! As you know Emily Blunt was offered the role of Back Widow in 'Iron Man 2' and she took it. Shortly after she accepted the role, all of a sudden Twentieth Century FOX swoops in and tells her she is going to co-star in the studios upcoming film 'Gulliver's Travels' that will be filming around the same time as 'Iron Man 2', since she is contractually obligated to FOX she may have to ditch out on 'Iron Man 2'. I have a conspiracy theory about this whole mess that you can read here.
If Emily Blunt for sure has to drop out of the Black Widow role it looks like Scarlett Johansson will be stepping in. EW reports:
...sources around Hollywood say Johansson has indeed met with the filmmakers and is interested in taking the role of Russian superspy Natasha Romanoff, who doubles as Black Widow. Blunt's reps are still trying to make both projects work, but Gulliver's is further along, with a start date of April 15.
I honestly don't see Johansson in the role of Black Widow, she doesn't really fit the character at all. To me she seems way to soft and pillowy. She doesn't seem like a girl that could go out and kick some ass or have that kind of super hero presence. But I guess if anyone can make a person into a super hero it's Jon Favreau, if he does turn her into Black Widow maybe he can turn her into a good actress as well.