Before exiting Arbil make sure that you have saved all your changes. This can easily be done by the key short-cut CTRL+S.
You can exit Arbil by closing the main window, or through file -> exit on Wi§ndows or Linux, or Arbil -> quit Arbil on Mac OS. In case of unsaved changes a message will appear and ask if you wish to save changes before exiting; choose yes or no, Arbil is now closed.