I don't quite know what you're trying to achieve or why? But the attached seems to me to be the appropriate response. You wouldn't so much seek to patch the missing area as to restore the surfaces to their untrimmed boundaries. The easiest way in this case may be the method that I have constructed, which was to extend the sides and just rebuild the blends.
Best Regards
Hudson
www.jamb.com.au
Nil Desperandum illegitimi non carborundum