I think Revit should automatically relinquish all elements when a user closes a workshared model. A user has to synchronize periodically and when closing anyway. If a user works for long without synchronizing and then closes the file, any changes lost will be problematic for that person. When elements are reserved by someone who forgot to relinquish and then left on holiday, it stops everybody else from doing their job, potentially for several days. I am working on a big project, and we are having issues with this on a weekly, if not daily basis.