No, if it can't find the default spot where the library is kept it changes it to Home folder/Music/iTunes. All of the songs on your hard drive will be accessed from the hard drive when plugged in (nothing will be copied onto the computer), but when the hard drive is not plugged in it will be up to you to manually copy the files over. Not sure if this can be done, but possibly look into Automator to do this automatically for you?