Mass Export all Projects - Is it possible?
Unfortunately, there's no way to Export all of the Projects to an MS Project file. This functionality is limited to one Project at a time.
If you wanted to Export as XML, you could do this pretty quickly assuming that you just want a backup of the Project, Project Tasks, and Dependencies.
You could go to each of the following table's List Views, Right-click the List Header and select Export > XML
Project Table - "pm_project"
Project Task Table - "pm_project_task"
Project Dependency Table - "planned_task_rel_planned_task"