It's also worth saying that PRH will have loads of other books on the go, being considered and bought, being edited, being copy-edited, having covers designed, going to the printers, being marketed, being sent out for review etc etc etc. At the moment there's nothing to 'do' with SW's past oeuvre which is out there in the world and still selling, but presumably not in need of any immediate decisions or actions by PRH.
It's impossible to know what stage OWH is at, given that we don't know what, if anything, SW is doing/being required to do to alter it. Maybe her editor already has a new MS to edit, and that may be a considerable job -- or maybe getting the MS is still some time away, so thinking about marketing it etc is in the future.
I do find myself speculating about SW's state of mind while writing/revising OWH. The two existing sequels to TSP benefited from a huge groundswell of the reading public's interest in what happened next and its goodwill (though it's also true that TWS has very obviously the signs of Difficult Second Album Syndrome, which you'd expect in trying to follow up a once-off).
But this will be the first time she's writing a book, if she's indeed writing/rewriting it, with a knowledge of a potentially actively hostile readership, or at least one containing previous fans who feel outraged and betrayed, and the likelihood of negative reviews, and that all reviews in newspapers, even positive ones, will reference the CH investigation.