Are you using a directory service such as Active Directory? If so, user accounts won't be stored on computers unless your settings create mobile accounts. You may want to consider removing the option to create mobile accounts in the Directory Utility application and you wouldn't need a script.
To get the name of the last user who logged on to a Mac you can use:
last -1 console | awk '{print $1}'
To get a list of local accounts that are part of the admin group you can use:
dscl . -read /Groups/admin GroupMembership
To remove a user from the Mac's local list of users you can use:
dscl . delete /Users/username
Putting this all together would look something like this:
#!/bin/sh
# Get last logged on user's name
LASTUSER=$( last -1 console | awk '{print $1}' )
# Test whether the LASTUSER is a member of the local admin group.
# Returns "1" if not a member
TESTLOCALADMIN=$( dscl . -read /Groups/admin GroupMembership | grep $LASTUSER )
# Delete last user
if [ $TESTLOCALADMIN = 1 ] ; then
dscl . delete /Users/$LASTUSER
fi
exit 0
I haven't tested. Someone else may have a more elegant way of doing this.
