I had to do a git history rewrite via "git filter-branch" and one other method. I can attest that you really have to go out of your way to actually permanently get rid of anything in a git repo. It's always funny to me when I see an engineer have a panic attack the first time they think they've trashed the repo and lost important code. They always have that same look as relief washes over them when I show them how to recover from the mistake.