Even if a bishop were to lay his hands on a woman and speak all the correct words of ordination, nothing happens. Same thing if a priest were to say the correct words of consecration at a Mass, but were to use oreo cookies and coca cola instead of unleavened bread and wine. Nothing happens.
The Pope issued Ordinatio Sacerdotalis, which says the Church can not ordain women, and that this is to be held definitively by all Catholics. This document met all of the criteria for an infallible, unchangeable statement by a Pope. It is now doctrine.
The definition of heresy is this: The obstinate post-baptismal denial of some truth which must be believed with divine and catholic faith, or it is likewise an obstinate doubt concerning the same.
Anyone who is guilty of heresy is a heretic, and the penalty for heresy is immediate, automatic excommunication,* latae sententae*.
Therefore, those who insist that the Church can ordain women, are denying a truth which must be believed with divine and catholic faith. They commit heresy, and are, therefore, heretics. They have been automatically excommunicated. They are no longer in communion with the Body of Christ, and, therefore, with Christ, because Christ and His Body are one.