We have an Automation in ServiceDesk to close a ticket when its approval is "Denied". This feature is available from 9315 builds of ServiceDesk Plus. In general, the technician had to manually close or change the status of a ticket when it is denied by the approver.
An admin of ServiceDesk can enable this option at [Admin tab -> request closing rules and enable "Close requests automatically if approval is denied." ]
Click here to know about this feature.