I am considering "alone" mode solution.
As far as I understand in Alone mode only one jar should be started, like: java -jar mysolution alone, and that's it?
In this version GUI should consist functionality to open database from file and perform all actions that usually Client did over network?
By "must not use networking in alone mode", you can understand that your RMI/Socket server must not be used when running the application locally. For instance, you can't start a server locally and use it in standalone mode. In fact, this would mean that you prepared your program only to run in networked mode.