Hi,
I'm afraid that a vendor won't have any change to unpublish himself.
Regarding the different registration settings ; you can have conflicts with the "manual validation" and also with the "automatic creation".
While in one case you can give the access to the vendor to approve himself, in the other case you provide a double bind while an account is published and his vendor not.
So for the moment, for such implementation in the HikaMarket core is declined.
Without knowing more about your configuration ; I can't give you a clear answer on the possibility using a plugin.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.