These files are updated everyday (if I do not forget, I append data to them: Copy/Paste from a web page from Safari into TextEdit).
I installed (on last Saturday ?) Mojave on an external HD, (one hour to wait !), and play a bit (download Firefox, Xojo 2015r1 and install them), run Disk Utilities (whatever its current name is), then shut down.
I do not recall when was the last day I appended text into those two files nor if there is more missing in action files, but when I wanted to update the files yerterday, they were no more in TextEdit / nor in my hard disk.
I booted some tens minutes ago on Mojave, made a search, but it does not found them.
The files have “Alley Oop” inside them / in their title (but a bit different).
Nota: I have other files that hold that name in their title, but they still are here. I also have plenty png file for that character.
I checked for invisibles files, but nothing. I also checked an archived folder just in case I moved them there, but no.