Do you think your enjoyment of the film will be hampered by the fact that we know that the rebels eventually DO get the plans? I usually hate backstories because we know how it ultimately ends, and any tension or drama that develops is typically irrelevant with regards to the larger story.
I think however, that it would be a significant plot twist if our main heroes actually FAIL at the end of the film, and it turns out that some other team ends up getting the plans. Imagine the audience is watching Rogue One the whole film, assuming the good guys will win, and it turns out they fail???