Documentation incorrectly claims merge request refs are deleted
Introduced in GitLab 13.4, 14 days after a merge request gets closed or merged, the merge request head ref is deleted. This means that the merge request isn’t available for local checkout from the merge request head ref anymore. The merge request can still be re-opened. If the merge request’s branch exists, you can still check out the branch, as it isn’t affected.
However, this behavior is behind a feature flag that is currently disabled. So merge request refs are not cleaned up, but the documentation says they are.