I'm very glad for the tourist picture of the collapse posted by Jo... the word landslide had created even greater horrors in my mind.
Now, what we've lost. By way of documentation, here is a picture I took of this wall nearly two years ago (incidentally on my birthday!). We might add some description and call this a brick quoined opus incertum wall, about three meters high with a slit window near the top. It existed between the last two doors (not numbered) in the eastern most insula of Regio III (7 or 8, depending on your map).
There are other items that could supplement this image. Jeremy, do you know of any archival images of this wall from your research? Perhaps Jennifer and Arthur Stephens have more precise and recent data from their via dell'Abbondanza project research.
Sadly, this kind of post-mortem documentation could become (and always could have been) a regular story.