Jewish Festivals: Ending: Before Havdala: Baruch HaMavdil and Birkat HaMazon

Saying Baruch ha'mavdil bein kodesh l'chol after dark at the end of a Jewish festival or of Rosh Hashana does not affect the additions you will then say in birkat ha'mazon.
Situation On a Jewish festival afternoon, you washed your hands, said ha'motzi, and started eating.  It is now dark and the end of the Jewish festival.
What To Do You may say Baruch ha'mavdil bein kodesh l'chol and do melacha, and then
  • Continue to eat your meal, or
  • Say birkat ha'mazon INCLUDING ya'aleh v'yavo and ha'rachaman hu yanchileinu yom she'kulo tov.