The leader of his church has the obligation to ask him if he endorses the sin of murder in the form of abortion, and if he affirms the sin he is not repentant and should be excommunicated.
If he attended my church and was public about it, he would likely not be permitted to receive the sacraments until such time as he repented, nor would he be allowed to exercise any sort of a leadership role (usher, lector, choir, parish council, ccd teacher, cyo coach, etc., etc.), but the only way I could see where he would be utterly shunned would be if he did something directly as a threat to public decency and order within a Mass: for example, if he got up and started cursing the homilist as he preached a pro-life homily, if he tried to steal the Body of Christ during communion, and so on.