Question: Was Vashti banished or was she murdered?
Answer: The book of Esther (1:19) only says that Vashti should “no longer come in to the king”, which might mean being banished or whatever. Our sages explain, though (see Rashi on that verse), that, in those days, for a wife to be banished from a king really meant execution. They had a rule that no one else would ever be allowed to marry her afterwards; that, they thought, would be a disgrace to the honor of the king. In order to insure that, she was killed.
Best wishes,
Michoel Reach