All right, first grab a list of all the accounts and put that list into a file called /root/acctlist:

grep -v 'root|#' /etc/trueuserowners | grep resellerusername | cut -d: -f1 > /root/acctlist


for i in `cat /root/acctlist` ;do /usr/local/cpanel/scripts/killacct $i --killdns=n --force ;done