Some feared the worst when rumors started swirling about Rogue One: A Star Wars Story having to undergo drastic reshoots, but if the news we're hearing now is accurate, the situation doesn't seem near as dire.
According to Makingstarwars.net sources, the general feeling around the reshoots internally is positive, and not a complete mad scramble. Those sources also say that Director Gareth Edwards is doing the reshoots side by side with Writer Christopher McQuarrie, who's final script is the one that the studio thought was superior to the original.
That new script is part of the reason the film was called "uneven" in its first cut, as McQuarrie's new script wasn't completed until after the first run had already been shot. When new drafts did come in, they would shoot those, and that led to the problem they have now. They are now adapting everything to that draft, hence the reshoots, which are supposedly totaling at least 40% of the film according to members of the crew.
Other tidbits include that 32 different sets have been recreated for the shoots and that the crew is working 6 days a week for 8 weeks to get it all done. Also, Director of Star Wars: Episode VII - The Force Awakens J.J. Abrams will reportedly be supervising the reshoots, to make sure the films coalesce as a whole.
With the reshoots factored in, the film looks to be right around the original proposed budget. Rogue One: A Star Wars Story is still slated for a December 16th release date.