Final Cut Pro- Reopen Library and Entire Timeline is Gone!
The timeline for which you are looking is actually called a "Project".  Projects are stored within events, which are in turn stored within a library.  Just opening a library (from within the finder, for instance) will not necessarily open your project.  To do that, you need to twirl down the disclosure triangle next to your Library in the event manager, select the event upon which you were working, and then double click the Project name to load it in the timeline.  Also, make sure that you are connected to any drives or network storage locations that you might have stored media to when you created the project.