How is Rosie Huntington Whiteley replacing Megan Fox in Transformers 3?

I mean, are they going to make Megan break up with Shia or will she die and then Rosie come in? Or are they going to be lame and just throw her in the movie like its nothing?How is Rosie Huntington Whiteley replacing Megan Fox in Transformers 3?Well there probably just going to say they just broke up, which is so lame cause they been through 2 battles together and Megan and Sam just go together.