They'll come all right, by any means they can find. What we need is a way to stop the undesirable ones. They are encamped in Calais, making constant illegal attempts to breach border control, they care not if they are wanted or not, many smell money, criminal activity with little redress, and an easy life at our expense.
People you are describing will try to come no matter whether UK is in the EU or out. As long as the living standard is higher here then where they from they will risk it.