We had guests come over just before Shabbas was out and they needed to leave asap, can one say havdallah before he has done ma’ariv and fulfil the mitzvah? (Do i have to redo havdallah after maariv, can i drink the havdallah wine?)

You can make Havdalah before Ma'ariv in such a situation. You are obliged to drink the wine and you do not have to repeat Havdalah after Ma'ariv. Rabbi Yosef Weitzen