On the Project Closing window, there is no way to determine if a timesheet that has charged to a project is still in workflow.  The project closing checklist is checked which tells me that the project is ready to be closed.  There should be a warning that there are some pending timesheets waiting to be approved if you try to close a project.

Under Review
Ideas Administrator

Thank you for your suggestion. We will consider this functionality for a future release.  

Best regards.