How to backup the Android calendar file (is there such a file)?
Android stores calender data (and contacts as well) into a SQLite database in the system. The format of that SQLite database differs between ROMs -- so at least for "normal users" it's not that good an idea to "simply" copy that SQLite file. Rather use a good backup app for this. A good example would be iCal Import/Export, which allows you to export your calendar to an .ics file -- and also to import from .ics files, e.g. for a restore.