Merge proposals are deleted when I delete my fork of a repo

[Adolfo Jayme Barrientos]

When you create a pull request on GitHub, it remains accessible even after you delete your fork. On Launchpad, MPs belong to your personal repo instead of the project repo it was copied from, so when you delete your personal repo after contributing a patch to a project repo, the merge proposal is deleted as well (though not the merged commits), so you lose the learnings from the people who reviewed your patch.