They are not in communion with the Catholic Church and they are already excommunicated. They have already excommunicated themselves by their behavior.
Excommunicated Catholics are still Catholics and remain bound by obligations such as attending Mass, even though they are barred from receiving the Eucharist and from taking an active part in the liturgy (reading, bringing the offerings, etc.). However, their communion with the Church is considered gravely impaired. In spite of that, they are urged to retain a relationship with the Church, as the goal is to encourage them to repent and return to active participation in it.