Can a brain dead person live after being taken off life support?

My friend took a bunch of pills and had no heartbeat for 6 minutes. The docs said she was in a coma and then after doing tests said she had no brain activity. She was taken off life support and still has not yet passed. They are moving her to hospice. So I guess my question is if she was brain dead woudnt she have passed soon after being taken off life support?