Only Security Administrators can remove users. In the example below, we display the current list of users and then remove the user spate. We then re-run the command to confirm that the removal took place. Note that you need to specify the username.

$ hicli user list
Username    Full Name               Privileges
---------------------------------------------------
secroot     Security Administrator  SEC_ADMIN
spate       Steve Pate              CLOUD_ADMIN
$ hicli user rm spate
$ hicli user list
Username    Full Name               Privileges
---------------------------------------------------
secroot     Security Administrator  SEC_ADMIN

Note that all objects (Cloud VM Sets and VMs) are owned by administrative groups and not by the users themselves. Thus, if you remove a user, the object will stay intact.