In terms of how this would be done practically: We did have intact gitolite logs I believe, which record the credentials involved in pushing any ref and what they're getting updated to, so we'd have known what data we would have needed to locate and who we could contact to provide it. And since the commit hashes describe their content, there wouldn't have been a risk of manipulated data.
Presumably the mirrors also did not run an aggressive 'git gc' immediately after 'git remote update', so they would still have non-corrupt commits in the object store, in which case you could recover by "just" resetting any corrupt refs.
