If Roe vs. Wade were to be overturned by judicial opinion, it would not make abortion illegal, it would simply revert back to the system in place before Roe vs. Wade, which left it in the hands of the states.
In order for abortion to become illegal, there would have to be a constitutional ammendment added, because Roe vs. Wade was decided upon an interpretation of the fourth ammendment. (The supossed grounds for the right to an abortion stem from the interpritation of the fourth ammendment as guaranting a "right to privacy", thus women's right to privacy trumps out the life of the unborn.) In order for there to be a constitutional ammendment, there has to be a purposal by congress or a national convention of atleast 66% of the states. Then after this, they must be ratified by conventions held in 75% of the states or the legislatures.
Roe vs Wade, could be overturned, but would likely be reinstated upon the apointment of Liberal activist judges at the supreme court sometime in the future. This is why for there to be any closure to abortion as a means of birth control, there must be a constitutional ammendment.