> put in some code that tries to detect whether parts of an article have been deleted and, when in doubt, keep the old version it live
Unlike deleted pages which are hidden from non-admins, deleted parts of articles are almost always reachable if you dig them out in the revision history of the page. The rare exceptions are for text which violates someone's copyright, or which is defamatory, all of which require manual intervention by an admin to be deleted for real. So this content is still archived by Wikipedia, and publicly available, just not very easy to browse.
Unlike deleted pages which are hidden from non-admins, deleted parts of articles are almost always reachable if you dig them out in the revision history of the page. The rare exceptions are for text which violates someone's copyright, or which is defamatory, all of which require manual intervention by an admin to be deleted for real. So this content is still archived by Wikipedia, and publicly available, just not very easy to browse.