I like those examples you gave–I find those clarifying.
If I keep around all deleted file SHAs, I could have a setting that you could enable that deletes those SHAs as they are encountered by sync. It certainly would be off by default, though.
Another idea to consider – kinda like how Windows has regular “delete” but also “permanently delete” if you hold Shift+Del, PhotoStructure could have regular “delete” that sends to recycle bin, but also “permanently delete including future zombies”.
Regardless, I would still prefer newly-imported assets to be automatically sent to a “zombie import purgatory” section of the recycle bin, instead of being immediately permanently deleted. It’s unlikely, but the SHA for two completely different images could accidentally match, so it’s safer for PhotoStructure to automatically quarantine the images rather than automatically delete them.
Good point: PhotoStructure uses SHA512 precisely to avoid collisions, though.