Per documention, I can delete all userdata using ./splunk clean userdata -f
http://docs.splunk.com/Documentation/Splunk/4.3.4/Admin/DeleteuserdatafromtheCLI
Question: will this affect the admin account?
It will reset the admin password back to "changeme", and I think all other admin user object fields (ie, full name, timezone, etc) back to defaults. But it will NOT delete anything in etc/user/admin. BTW, it will not delete the etc/user/... dir for a user who has created any private objects (saved searches, etc) and those private objects will still exist in that path.