Thank you for posting. I would be a hypocrite not to feel for Royal Ballet goers who bought tickets planning to see her in A Month in the Country, but I, too, am just delighted by this news...(No guarantees of course for any performance, but at least now I'm not only scheduled to see her with Sarafanov in Giselle, but I don't feel like a chump.)
NB: Osipova has changed her dates for her November MONTH IN THE COUNTRY performances with the Royal Ballet and will be performing on 5th November rather than 12th November (when that role will be danced by Yanowsky). Consequently, she will, I assume, be entirely free to dance the Giselles with that dancer's dancer Leonid Sarafanov in New York.
Luckily for RB goers, ROH allows ticket holders to return tickets and the ROH will try to resell them. When I was in London this August, I returned a pair of Swan a Lake tickets when Stepanova was replaced by Skorik. The ROH was very pleasant about it, my tickets were resold and I got my money back.