Hi,
The goal of the guest checkout is to not have an account.
Which means that the guest account cannot be re-used and the customer will have to re-enter his details if he loose his session.
If you want to let the user have a password ; it means that you want to use a Joomla account. So it would not be a guest checkout but a classical registration.
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.