Reading the code, I wonder why rvg_delete_orphans() deletes auto-drafts *unless* the auto-draft has postmeta data ?
Is the meta used when restoring an auto-draft?
I searched a few WP databases for auto-drafts with postmeta data and found only one distinct meta_key, added by a plugin (WordPress SEO by Yoast).
Also, what about categories, do those need to be handled? I posted some code here about revision deletion and categories, and also custom taxonomies: http://wordpress.org/support/topic/deleting-post-revisions-do-not-use-the-abc-join-code-you-see-everywhere