Admins can choose to have all work orders automatically close X days after they are marked completed by the assigned user!
To do so, go to the left navigation bar > Settings > Advanced > General > Work Order Workflow.
At the bottom select the toggle under "Automatically close completed Work Orders after [XX] days"
Once selected, 7 day(s) is the default and you can change to any number of days you choose
Then, click Save and you will see the following