In https://gerrit.wikimedia.org/r/#/c/243699/, Daniel said
Yesterday we realized that we should actually not drop usage tracking for deleted entities: we need the tracking entries so we know which pages to re-render when the entity is restored. This is analogous to the fact that we store red links in pagelinks.
Maybe they should get a different usage or modified usage so that these 'usages' can be filtered out when generating stats and so that people can find them.
We should figure out how we want to handle deletions...