Q. Can a person be excommunicated from the Jewish people?
A. The short answer is no. The Talmud says that a Jew who has sinned is still a Jew.
There were various forms of ban imposed from the time of the Talmud onwards as communal punishments for offences of varying degrees of severity. The most serious effect was that a person was not allowed to participate in Jewish community or synagogue life. But though this brought hardship to the person concerned, they remained Jewish.
These days, if people bring Judaism and the Jewish people into grave disrepute, we may decide to deny them any official position or honour within the community, but they are still Jewish.