Thank you for pointing that out. Due to a design flaw in the vBulletin "multiple" DM, the previous edit I posted should not be used, as I think it will cause incorrect membergroups to be saved when deleting more than 1 moderator at once (like if you delete an area that has 2 moderators on it).
For the next release, the method will be the same as deleting an entire usergroup in vBulletin, to skip the user DM entirely and just update the raw database fields for the user. This will be as efficient as a multiple-DM, but will be unable to change any related data using plugins when removing the user from the moderator group. I think this should be acceptable, since the behavior is the same when deleting a usergroup -- a situation where vBulletin should have used a multiple-DM themselves if it was designed properly.