I've had a similar issue in the past with the donation plugin that use to be on here
http://www.forumcoding.com/re-instal...ware-security/
So when i upgraded from vb 3.7.x to vb 4.2.x, i faced similar issues with tables being dropped and i had a Database error which prevented me from accessing the forum, when i tried to get rid of the plugin, i couldn't it uninstall it because of a missing table.
What i did is that i disabled hook through config.php by adding this line in the beginning
define('DISABLE_HOOKS', 1);
or you can disable it via admin cp if you can access it. Admin CP -> vBulletin Options -> Plugin/Hook System -> Enable Plugin/Hook System
Once i disabled the hook, i could access the forum without seeing the database error. I uninstall the plugin, or i think i reinstall it then i uninstall it, and that got rid of the plugin's table without needing to restore a back up.