When a work item is reset or deleted, the time entries that were linked to it will still exist.
When a work item is reset, its related tasks, work team, budget and estimated time will all reset to either the previous work item in the schedule or the template. The time entered on that piece of work will not be reset, however. Any time entries will remain under 'Time Entry Report' for that work item and the related contact.
When you delete a work item, the time entered will still exist. However, in order to view any time entries, you will need to navigate to the contact that the work was created from, and view within the Time & Budgets tab of the contact.