they are still there as tags. If you want to “reactivate” them, just create a new branch from the tag:
Most of them were unused (because we did not always delete them at reintegrate), so we just moved them to history as tags.
In general I have private branches in my local checkout. I name them “private/LUCENE-xxxx” and never push them. For larger changes where more than one person works on, we can push branches, but as discussed before, they should follow a naming convention and should not be top-level.