I think its just a 3 dimensional snapshot of a scene. Whether it tells a story or not has no relavence of whether or not its a diorama. Now only the viewer can determine if its good or not if it happens to appeal to their individual aesthetic. There are socially or group accepted "themes" i.e. does it tell a story? Does it make the viewer make up his own story? Is it a recording of a moment in time? By no means is their a set definition of a diorama outside of what in the relavence of this discussion would be from an IPMS definition of what a diorama is. Vespa Boys "scenes" in themselves can be considered diorama as they are comprised of elements that themselves are the subject of the scene. Manhole covers, rocks, painted lines, curbs etc are rendered three dimensionaly (in the case of the painted lines they are painted over ground effects or materials and making them integral to the scene itself.)
Diorama are no where near dying. In this genre or others. Architectural firms, engineering firms, logistical firms (I built a model of the Titan IV Launch Vehicle assembly building and maquettes of equipment so that we could figure out ways to move large test equipment and launch vehicles more efficiently. That could be considered a diorama), theatre companies (stage shows) use them all the time to work out stage changes and prop movement. Museums, tradeshows, marketing agencies, film companies, educational institutions, etc all incorporate dioramas into their everyday workings.
I guess if you look at it in a simpler aspect, kids playing with their toys in the dirt, little girls playing with their doll houses, nativity scenes, the arrangement of ones toys in the room or even the decoration of that room, mobiles placed over the crib, all have given us exposure and experience with dioramas from our earliest memories. Its only natural that we now, as model builders, use that early learned experience as a creative outlet and a means to display our handy work, So actually we are, or at least should be, predisposed to think of dioramas as only natural. Thus the dying part comes from those that "don't want to" rather than any form of "can't".
Now if we are talking the original 19th c. dioramas....then yes, they are dying if not already dead. Originally they were cleverly lit paintings on canvas and linen that would move or the stage would move to give the viewers a sense of moving through scenes or time. Season changes, fantastic worlds, landscapes, recreated battles or mythological plays were all the subjects of these dioramas cleverly lit and allowing the viewer to pass through or view the change and be left with a sense of being there. Sort of like a more modern stage scrim or prosceneum that if lit from one side looks solid and when lit from behind can reveal what is behind it and change the scene all together. Louis Daguerre was the best known and considered the inventor of these dioramas and was the inventor of his name sake the Daguerretype (early photography).
Mike
"Imagination is the dye that colors our lives"
Marcus Aurellius
A good friend will come and bail you out of jail...but, a true friend will be sitting next to you saying, "Damn...that was fun!"