There is no central authority, so no one can expel buddhists from buddhism.
However, I think there is excomunication of troublesome monks. I remember the Buddha talking about killing someone "in this doctrine and discipline". He was talking about a monk who thought that a woman's touch was no different from a pillow's touch. The "killing" consists of stop talking to the troublesome monk. I think in this case that the monk changed his views and was welcomed back.
Off course, today only a subset of monks can excomunicate another monk. So it doesn't mean he is expelled from buddhism. He is excluded from that group alone.
I don't know the vinaya well, so this post is not very trustworthy.
He turns his mind away from those phenomena, and having done so, inclines his mind to the property of deathlessness: 'This is peace, this is exquisite — the resolution of all fabrications; the relinquishment of all acquisitions; the ending of craving; dispassion; cessation; Unbinding.'
(Jhana Sutta - Thanissaro Bhikkhu translation)