I'm a member of 5 websites, including this one. I have never been banned from any - once had a post deleted from one because I included too many asterisks (I was paraphrasing a humorous scenario at the time but - "rules is rules")
. One, I don't post on much - but that's because it's a crap site anyway.
It has never entered my head to make a dramatic exit. If I felt I couldn't post any more I would just - stop posting. Wouldn't it be awful to announce you were leaving - and nobody begged you not to? I wouldn't take the risk.