This depends on how you delete the employee. There are three scenarios:

1. If you select 'Edit' within the employee card and change their status to 'Archived' (shown below) this will change their associated user account status to 'Disabled' preventing them from logging in. Changing their status in the employee file back to 'Current' will then re-enable the account access or you can manually re-enable the account under Company Users.
2. If you delete an employee after completing step 1, this will delete their associated user account - This cannot be reversed.
3. If you make an employee a leaver, this will also delete their associated user account - This cannot be reversed.