So, can you rebuild a catalog from a cache file in Elements 12 Organizer or some other way?
Let's go directly to that question: the answer is no, unfortunately. The cache file 'thumb.5.cache' is an sqlite database storing your thumbnails in very small dimensions (max 320 x 240 pixels) and in a binary format...
What is curious in your case is that your catalog folder seems empty apart from that cache. You have 'optimized', which should have rebuilt the cache.
I suppose you did search for folders containing a 'catalog.pse12db' database file?
I searched the entire computer, (3 hard drives and 2 external hard drives) for the .pse12db and never could find the one I needed. I found one in the file where it should have been but it had no photos associated with it.
However, I searched all the hardrives for any .tly files and found a backup that I must have done which crashed in the process. Crazy thing, it was just at C:backup.tly, not even in a folder or the F drive where all the photos and other adobe files are kept. After running that backup for 40min., almost all was restored. I'm happy. I'm sure one way or another it was all my fault (or someone else in the family closing it without knowing), I'm just glad the adobe organizer was able to correct it.
Thanks, all's well!