Luckily for me my hosting provider (Media Temple) was able to recover the file from their backups in a timely manner, fully resolving the issue. From what I've read, if you cannot restore the file yourself you must repair plesk either by reinstalling the same version or upgrading. I am still unsure what information is lost in doing so however.
The symptoms of removing the file are: Plesk, FTP, MySQL, SSH all work fine, your subscriptions are visible, site files are still intact - but you get the default CentOS server page on any domain pointing to your server.
(I guess I can't choose this as an answer just yet. If anyone has a more detailed answer with a way to restore plesk to working condition WITHOUT using a backup, I will transfer correct answer to you!)