The Queen is known to be fond of Sarah. Prince Philip loathes her, and he’s the final word in all family matters of this sort. But he’s also 96 and probably slightly dotty by this point and had cut down public appearances. He could probably stay home for the wedding and it could be easily explained as one of his illnesses.
I also doubt that Sarah would get her HRH back. However I think she will get her original style back, instead of Sarah, Duchess of York (which is just basically a surname now) she might go back to being THE Duchess of York. Instead of HRH she might be styled “Her Grace” as the wife of a non royal duke does.
So Her Grace The Duchess of York isn’t such a bad deal.
Of course this won’t happen but it’s a fun fantasy. Sarah’s a hot mess but I like her. I hope she comes out in the end with Andrew.