The vagueness seems benevolently intentional.
This could mean a polite rejection, or that they will review the application in case all preferred candidates reject the actual job offer (or quit or give reasons for termination), or that they might indeed review old applications if a second, identical job is vacant.
Option 3 is likely very rare.
In some localities, there also might be legal necessity for them to notify you when they reserve option 2 or 3 instead of sending back/destroying your application - alternatively, they might perfectly well intend to destroy it but want to avoid both the impoliteness and the hassle of not returning it (which might be considered impolite in some localities).
The vagueness is there so that absolutely no promise or commitment to do or not to any of these can be implied and used as a reason to pester them or even seek legal action.