[Campion]

Is there evidence in the NT where someone who receives the Holy Spirit and then the Holy Spirit departs them?

If you mean an anecdote about a specific, named person, I doubt it.

However, I don't think the texts I posted from Hebrews 6 and Hebrews 10 are describing a situation which can't actually occur, or didn't actually occur.

[redleghunter]

I agree. The Hebrews references deal with the parable of the soils and also apostasy. It seems by the language the apostasy is not just sinning but turning and denying Christ.