I think any way you want to look at this passage it is clear you can be cut off.
Second, 'being cut off' has nothing to do with losing one's eternal salvation.
In the passage, the Jews are unsaved not saved who became unsaved.
It is speaking of God turning once again to focus on the Jew instead of the Gentile in giving the Gospel
You don't work to get saved and you don't work to stay saved.