Free Edition GDPR mandates that all personal data regarding the data subject should be erased once the purpose for processing is completed. One of the few exceptions being legal purposes.
The same principle is followed in Endpoint Central as well. Upon deletion of technicians, Endpoint Central will not retain any personal data except for the user name of technicians. Since a technician would have carried out certain tasks using the Endpoint Central server (eg. remote troubleshooting a computer), it is essential for audit and legal purposes to maintain a log of the tasks carried out by that particular technician.