Why sadder and more drastic?
Anna neither ends up as a whore on the streets, nor does she become a drug addict, nor is she sold as a third wife to a tribe chief in Africa or the Amazon (Which has already been suggested here and which no one found drastic.)
I just took the information available about the existing characters, weighed the whole thing against Anna's wishes and ideas for a wonderful life (by that I don't mean her sexual wishes) and came up with a plausible scenario for me.
As I have written before, there is currently no way for David to be redeemed in
Mr Palmer's story in which Anna does not benefit maximally from the intrigue and nothing happens to her.
That was the starting point and then I just took what already existed in terms of content and characters.
I actually only see one thing from the reactions to my post - that all the hard pro-NTR fighters who despise vanilla lovers are incurable romantics. At the end of the story they want Anna to drive off into the sunset with the man they favor and into a new romantic life.